Quick Snort Setup Instructions for New Users



  • Good Afternoon,

    I have configured Snort according to the guide & everything works great on the WAN.  I have created a LAN Interface & mirrored the rules for both.  When I go to start Snort on the LAN, I am getting the following error:

    snort[93176]: server /usr/pbi/snort-amd64/etc/snort/appid//odp/lua/service_EIP.lua: error validating …snort-amd64/etc/snort/appid//odp/libs/DetectorCommon.lua:318: table index is nil

    I have searched for documentation on this, but have been unable to find out what it is &/or why Snort will not start on the LAN interface.  Any guidance or suggestions would be greatly appreciated.

    Best-

    Darren



  • @darrenkdean:

    Good Afternoon,

    I have configured Snort according to the guide & everything works great on the WAN.  I have created a LAN Interface & mirrored the rules for both.  When I go to start Snort on the LAN, I am getting the following error:

    snort[93176]: server /usr/pbi/snort-amd64/etc/snort/appid//odp/lua/service_EIP.lua: error validating …snort-amd64/etc/snort/appid//odp/libs/DetectorCommon.lua:318: table index is nil

    I have searched for documentation on this, but have been unable to find out what it is &/or why Snort will not start on the LAN interface.  Any guidance or suggestions would be greatly appreciated.

    Best-

    Darren

    Confirmed. My system log is filled with this too:

    snort[4022]: server /usr/pbi/snort-amd64/etc/snort/appid//odp/lua/service_EIP.lua: error validating ...snort-amd64/etc/snort/appid//odp/libs/DetectorCommon.lua:318: table index is nil
    

    Snort starts on all interfaces 'though, yet it is cluttering up the logs with this constantly repeating message.

    pfSense 2.1.5 X64, Snort 2.9.7.0 pkg 3.2.3



  • @darrenkdean:

    Good Afternoon,

    I have configured Snort according to the guide & everything works great on the WAN.  I have created a LAN Interface & mirrored the rules for both.  When I go to start Snort on the LAN, I am getting the following error:

    snort[93176]: server /usr/pbi/snort-amd64/etc/snort/appid//odp/lua/service_EIP.lua: error validating …snort-amd64/etc/snort/appid//odp/libs/DetectorCommon.lua:318: table index is nil

    I have searched for documentation on this, but have been unable to find out what it is &/or why Snort will not start on the LAN interface.  Any guidance or suggestions would be greatly appreciated.

    Best-

    Darren

    It would be better if you start a new thread in the IDS/IPS sub-forum.  This thread was designed to contain just the how-to instructions.

    The answer to your problem is also posted in a previous thread here: https://forum.pfsense.org/index.php?topic=89393.msg495651#msg495651, but I will repeat it here.  This is a known syntax error in the OpenAppID rules package from the Snort VRT.  They committed to fix it in a mailing list post about two weeks ago.  It appears they have not yet.  You can disable the OpenAppID preprocessor to make the error go away.  Unless you have also written your own custom rules to use the OpenAppID signatures, they aren't working anyway.

    Bill



  • Very simple guide bmeeks, thank you for taking the time to explain this to us new users. Followed another guide and I kept having snort ban websites I was visiting.


  • Banned

    Hi!

    How about adding a little bit of info specific to nano users running snort? ;-)

    Maybe somethink like this:

    https://forum.pfsense.org/index.php?topic=106725.msg594731#msg594731

    Regards

    chemlud



  • Hi bmeeks/jflsakfja,

    This post was originally done a few years ago, how valid is the setup in post 1 and the rule configuration in post 3 these days?



  • Hey. Thanks for this useful post.
    Btw this list is 3 years old. Is it still (mostly) up to date ?

    Also I have a few repeating alerts I can't figure out. Can you help ?

    1:2018959.  ET POLICY PE EXE or DLL Windows file download HTTP
    1:28039.    INDICATOR-COMPROMISE Suspicious .pw dns query
    119:33.  (http_inspect) UNESCAPED SPACE IN HTTP URI

    Thanks !

    @jflsakfja:

    The Missing Part to Quick Snort Setup Instructions for New Users

    In tab "Rules", under "Category" select:
    (–- means blank table at time of writing)

    DONE > emerging-activex > all

    DONE > emerging-attack_responses > all

    DONE > emerging-botcc > all

    DONE > emerging-chat > all except:
    2010784 ET CHAT Facebook Chat (send message)
    2010785 ET CHAT Facebook Chat (buddy list)
    2010786 ET CHAT Facebook Chat (settings)
    2010819 ET CHAT Facebook Chat using XMPP
    2002327 ET CHAT Google Talk (Jabber) Client Login
    2002334 ET CHAT Google IM traffic Jabber client sign-on
    2001241 ET CHAT MSN file transfer request
    2001242 ET CHAT MSN file transfer accept
    2001243 ET CHAT MSN file transfer reject
    2001682 ET CHAT MSN IM Poll via HTTP
    2002192 ET CHAT MSN status change
    2008289 ET CHAT Possible MSN Messenger File Transfer
    2009375 ET CHAT General MSN Chat Activity
    2009376 ET CHAT MSN User-Agent Activity

    DONE > emerging-ciarmy > all

    DONE > emerging-compromised > all

    DONE > emerging-current_events > all

    DONE > emerging-deleted > ---

    DONE > emerging-dns > all except:
    2008446 ET DNS Excessive DNS Responses with 1 or more RR's (100+ in 10
    seconds) - possible Cache Poisoning Attempt
    2008470 ET DNS Excessive NXDOMAIN responses - Possible DNS Backscatter or Domain Generation Algorithm Lookups
    2001117 ET DNS Standard query response, Name Error

    DONE > emerging-dos > all

    DONE > emerging-drop > all

    DONE > emerging-dshield > all

    DONE > emerging-exploit > all except:
    2001058 ET EXPLOIT libpng tRNS overflow attempt
    2002913 ET EXPLOIT VNC Client response
    2002914 ET EXPLOIT VNC Server VNC Auth Offer
    2002919 ET EXPLOIT VNC Good Authentication Reply
    2002915 ET EXPLOIT VNC Authentication Reply
    2002758 ET EXPLOIT WMF Escape Record Exploit - Version 1
    2002742 ET EXPLOIT WMF Escape Record Exploit - Version 3

    DONE > emerging-ftp > all

    DONE > emerging-games > all

    DONE > emerging-icmp > ---

    DONE > emerging-icmp_info > ---

    DONE > emerging-imap > ---

    DONE > emerging-inappropriate > all except:
    2002925 ET INAPPROPRIATE Google Image Search, Safe Mode Off
    2001608 ET INAPPROPRIATE Likely Porn

    DONE > emerging-info > all except:
    2014472 ET INFO JAVA - Java Archive Download
    2014473 ET INFO JAVA - Java Archive Download By Vulnerable Client
    2014819 ET INFO Packed Executable Download
    2015016 ET INFO FTP STOR to External Network
    2015561 ET INFO PDF Using CCITTFax Filter
    2015744 ET INFO EXE IsDebuggerPresent (Used in Malware Anti-Debugging)
    2016360 ET INFO JAVA - ClassID
    2016361 ET INFO JAVA - ClassID
    2016404 ET INFO MPEG Download Over HTTP (1)

    DONE > emerging-malware > all except:
    2008438 ET MALWARE Possible Windows executable sent when remote host claims to send a Text File

    DONE > emerging-misc > all

    DONE > emerging-mobile_malware > all except:
    2012251 ET MOBILE_MALWARE Google Android Device HTTP Request
    2012848 ET MOBILE_MALWARE Possible Mobile Malware POST of IMEI International Mobile Equipment Identity in URI

    DONE > emerging-netbios > all

    DONE > emerging-p2p > all except:
    2000369 ET P2P BitTorrent Announce
    2007727 ET P2P possible torrent download
    2008581 ET P2P BitTorrent DHT ping request
    2008583 ET P2P BitTorrent DHT nodes reply
    2008585 ET P2P BitTorrent DHT announce_peers request
    2010144 ET P2P Vuze BT UDP Connection (5)
    2011699 ET P2P Bittorrent P2P Client User-Agent (Transmission/1.x)

    *emerging-policy > all except:
    2000419 ET POLICY PE EXE or DLL Windows file download
    2000428 ET POLICY ZIP file download
    2001115 ET POLICY MSI (microsoft installer file) download
    2003595 ET POLICY exe download via HTTP - Informational
    2001898 ET POLICY eBay Bid Placed
    2001907 ET POLICY eBay Placing Item for sale
    2001908 ET POLICY eBay View Item
    2001909 ET POLICY eBay Watch This Item
    2003303 ET POLICY FTP Login Attempt (non-anonymous)
    2003410 ET POLICY FTP Login Successful
    2003121 ET POLICY docs.google.com Activity
    2003597 ET POLICY Google Calendar in Use
    2002801 ET POLICY Google Desktop User-Agent Detected
    2002838 ET POLICY Google Search Appliance browsing the Internet
    2000035 ET POLICY Hotmail Inbox Access
    2000036 ET POLICY Hotmail Message Access
    2000037 ET POLICY Hotmail Compose Message Access
    2000038 ET POLICY Hotmail Compose Message Submit
    2000039 ET POLICY Hotmail Compose Message Submit Data
    2008238 ET POLICY Hotmail Inbox Access
    2008239 ET POLICY Hotmail Message Access
    2008240 ET POLICY Hotmail Compose Message Access
    2008242 ET POLICY Hotmail Access Full Mode
    2006408 ET POLICY HTTP Request on Unusual Port Possibly Hostile
    2006409 ET POLICY HTTP POST on unusual Port Possibly Hostile
    2002330 ET POLICY Google Talk TLS Client Traffic
    2002332 ET POLICY Google IM traffic Windows client user sign-on
    2002333 ET POLICY Google IM traffic friend invited
    2002878 ET POLICY iTunes User Agent
    2002722 ET POLICY MP3 File Transfer Outbound
    2002723 ET POLICY MP3 File Transfer Inbound
    2001114 ET POLICY Mozilla XPI install files download
    2001973 ET POLICY SSH Server Banner Detected on Expected Port
    2001974 ET POLICY SSH Client Banner Detected on Expected Port
    2001975 ET POLICY SSHv2 Server KEX Detected on Expected Port
    2001976 ET POLICY SSHv2 Client KEX Detected on Expected Port
    2001977 ET POLICY SSHv2 Client New Keys detected on Expected Port
    2001978 ET POLICY SSH session in progress on Expected Port
    2001979 ET POLICY SSH Server Banner Detected on Unusual Port
    2001980 ET POLICY SSH Client Banner Detected on Unusual Port
    2001981 ET POLICY SSHv2 Server KEX Detected on Unusual Port
    2001982 ET POLICY SSHv2 Client KEX Detected on Unusual Port
    2001983 ET POLICY SSHv2 Client New Keys Detected on Unusual Port
    2001984 ET POLICY SSH session in progress on Unusual Port
    2013031 ET POLICY Python-urllib/ Suspicious User Agent
    2013414 ET POLICY Executable served from Amazon S3
    2014297 ET POLICY Vulnerable Java Version 1.7.x Detected
    2012647 ET POLICY Dropbox.com Offsite File Backup in Use
    2012648 ET POLICY Dropbox Client Broadcasting
    2014313 ET POLICY Executable Download From DropBox

    DONE > emerging-pop3 > ---

    DONE > emerging-rbn-malvertisers > all

    DONE > emerging-rbn > all

    DONE > emerging-rpc > ---

    DONE > emerging-scada > all

    DONE > emerging-scan > all except
    2002992 ET SCAN Rapid POP3 Connections - Possible Brute Force Attack
    2002993 ET SCAN Rapid POP3S Connections - Possible Brute Force Attack
    2002994 ET SCAN Rapid IMAP Connections - Possible Brute Force Attack
    2002995 ET SCAN Rapid IMAPS Connections - Possible Brute Force Attack

    DONE > emerging-shellcode > all except
    2011803 ET SHELLCODE Possible TCP x86 JMP to CALL Shellcode Detected
    2012252 ET SHELLCODE Common 0a0a0a0a Heap Spray String
    2012257 ET SHELLCODE Common %0c%0c%0c%0c Heap Spray String
    2012510 ET SHELLCODE UTF-8/16 Encoded Shellcode
    2013222 ET SHELLCODE Excessive Use of HeapLib Objects Likely Malicious Heap Spray Attempt
    2013267 ET SHELLCODE Hex Obfuscated JavaScript Heap Spray 0a0a0a0a

    DONE > emerging-smtp > all

    DONE > emerging-snmp > all

    DONE > emerging-sql > all

    DONE > emerging-telnet > all

    DONE > emerging-tftp > all

    DONE > emerging-tor > all

    emerging-trojan > all except

    DONE > emerging-user_agents > all except:
    2010697 ET USER_AGENTS Suspicious User-Agent Beginning with digits - Likely spyware/trojan

    DONE > emerging-voip > all

    DONE > emerging-web_client > all except
    2011347 ET WEB_CLIENT Possible String.FromCharCode Javascript Obfuscation Attempt
    2011507 ET WEB_CLIENT PDF With Embedded File
    2010518 ET WEB_CLIENT Possible HTTP 404 XSS Attempt (External Source)
    2012119 ET WEB_CLIENT Possible Hex Obfuscation Usage On Webpage
    2012205 ET WEB_CLIENT Possible Malicious String.fromCharCode with charCodeAt String
    2012266 ET WEB_CLIENT Hex Obfuscation of unescape % Encoding
    2012272 ET WEB_CLIENT Hex Obfuscation of eval % Encoding
    2012398 ET WEB_CLIENT Hex Obfuscation of replace Javascript Function % Encoding

    DONE > emerging-web_server > all except
    2003099 ET WEB_SERVER Poison Null Byte

    emerging-web_specific_apps > all except:
    2010890 ET WEB_SPECIFIC_APPS phpBB3 registration (Step1 GET)
    2010891 ET WEB_SPECIFIC_APPS phpBB3 registration (Step2 POST)
    2010892 ET WEB_SPECIFIC_APPS phpBB3 registration (Step3 GET)
    2010893 ET WEB_SPECIFIC_APPS phpBB3 registration (Step4 POST)

    DONE > emerging-worm > all

    DONE > GPLv2 community rules > all except
    254 DNS SPOOF query response with TTL of 1 min. and no authority
    384 PROTOCOL-ICMP PING
    385 PROTOCOL-ICMP traceroute
    399 PROTOCOL-ICMP Destination Unreachable Host Unreachable
    402 PROTOCOL-ICMP Destination Unreachable Port Unreachable
    408 PROTOCOL-ICMP Echo Reply
    540 POLICY-SOCIAL Microsoft MSN message
    648 INDICATOR-SHELLCODE x86 NOOP
    649 INDICATOR-SHELLCODE x86 setgid 0
    1200 INDICATOR-COMPROMISE Invalid URL
    1201 INDICATOR-COMPROMISE 403 Forbidden
    1292 INDICATOR-COMPROMISE directory listing
    1390 INDICATOR-SHELLCODE x86 inc ebx NOOP
    1394 INDICATOR-SHELLCODE x86 inc ecx NOOP
    1437 FILE-IDENTIFY Microsoft Windows Media download detected
    1841 FILE-OTHER Oracle Javascript URL host spoofing attempt
    1846 POLICY-MULTIMEDIA vncviewer Java applet download attempt
    1852 SERVER-WEBAPP robots.txt access
    1986 POLICY-SOCIAL Microsoft MSN outbound file transfer request
    1988 POLICY-SOCIAL Microsoft MSN outbound file transfer accept
    1989 POLICY-SOCIAL Microsoft MSN outbound file transfer rejected
    1990 POLICY-SOCIAL Microsoft MSN user search
    1991 POLICY-SOCIAL Microsoft MSN login attempt
    2180 PUA-P2P BitTorrent announce request
    2181 PUA-P2P BitTorrent transfer
    2707 FILE-IMAGE JPEG parser multipacket heap overflow
    3463 SERVER-WEBAPP awstats access
    25518 OS-OTHER Apple iPod User-Agent detected
    25519 OS-OTHER Apple iPad User-Agent detected
    25520 OS-OTHER Apple iPhone User-Agent detected
    25521 OS-OTHER Android User-Agent detected
    25522 OS-OTHER Nokia User-Agent detected
    25523 OS-OTHER Samsung User-Agent detected
    25524 OS-OTHER Kindle User-Agent detected
    25525 OS-OTHER Nintendo User-Agent detected

    *IPS Policy - Security > all except
    4152 BROWSER-PLUGINS Microsoft Windows Media Player 6.4 ActiveX object access
    19436 BROWSER-IE Microsoft Internet Explorer CStyleSheetRule array memory corruption attempt

    Suppression List:
    #GLOBAL

    gen_id 1

    suppress gen_id 1, sig_id 536
    suppress gen_id 1, sig_id 648
    suppress gen_id 1, sig_id 653
    suppress gen_id 1, sig_id 1390
    suppress gen_id 1, sig_id 2452
    suppress gen_id 1, sig_id 11192
    suppress gen_id 1, sig_id 15306
    suppress gen_id 1, sig_id 16313
    suppress gen_id 1, sig_id 17458
    suppress gen_id 1, sig_id 20583
    suppress gen_id 1, sig_id 23098
    suppress gen_id 1, sig_id 2000334
    suppress gen_id 1, sig_id 2008120
    suppress gen_id 1, sig_id 2010516
    suppress gen_id 1, sig_id 20122758
    suppress gen_id 1, sig_id 2014518
    suppress gen_id 1, sig_id 2014520
    suppress gen_id 1, sig_id 2100366
    suppress gen_id 1, sig_id 2100368
    suppress gen_id 1, sig_id 2100651
    suppress gen_id 1, sig_id 2101390
    suppress gen_id 1, sig_id 2101424
    suppress gen_id 1, sig_id 2102314
    suppress gen_id 1, sig_id 2103134
    suppress gen_id 1, sig_id 2500056
    suppress gen_id 1, sig_id 100000230
    suppress gen_id 3, sig_id 14772
    #(http_inspect) DOUBLE DECODING ATTACK
    suppress gen_id 119, sig_id 2
    #(http_inspect) BARE BYTE UNICODE ENCODING
    suppress gen_id 119, sig_id 4
    #(http_inspect) IIS UNICODE CODEPOINT ENCODING
    suppress gen_id 119, sig_id 7
    #(http_inspect) NON-RFC DEFINED CHAR [**]
    suppress gen_id 119, sig_id 14
    #(http_inspect) UNKNOWN METHOD
    suppress gen_id 119, sig_id 31
    #(http_inspect) SIMPLE REQUEST
    suppress gen_id 119, sig_id 32
    #(http_inspect) NO CONTENT-LENGTH OR TRANSFER-ENCODING IN HTTP RESPONSE
    suppress gen_id 120, sig_id 2
    #(http_inspect) NO CONTENT-LENGTH OR TRANSFER-ENCODING IN HTTP RESPONSE
    suppress gen_id 120, sig_id 3
    #(http_inspect) HTTP RESPONSE HAS UTF CHARSET WHICH FAILED TO NORMALIZE
    suppress gen_id 120, sig_id 4
    #(http_inspect) HTTP RESPONSE GZIP DECOMPRESSION FAILED
    suppress gen_id 120, sig_id 6
    #(http_inspect) INVALID CONTENT-LENGTH OR CHUNK SIZE
    suppress gen_id 120, sig_id 8
    #(http_inspect) JAVASCRIPT OBFUSCATION LEVELS EXCEEDS 1
    suppress gen_id 120, sig_id 9

    Unknown

    suppress gen_id 120, sig_id 10
    #(smtp) Attempted response buffer overflow: 1448 chars
    suppress gen_id 124, sig_id 3
    #(ftp_telnet) Invalid FTP Command
    suppress gen_id 125, sig_id 2
    #(ssp_ssl) Invalid Client HELLO after Server HELLO Detected
    suppress gen_id 137, sig_id 1
    #(IMAP) Unknown IMAP4 command
    suppress gen_id 141, sig_id 1



  • @THS:

    Hey. Thanks for this useful post.
    Btw this list is 3 years old. Is it still (mostly) up to date ?

    Also I have a few repeating alerts I can't figure out. Can you help ?

    1:2018959.  ET POLICY PE EXE or DLL Windows file download HTTP
    1:28039.    INDICATOR-COMPROMISE Suspicious .pw dns query
    119:33.  (http_inspect) UNESCAPED SPACE IN HTTP URI

    Thanks !

    A few options may have had slight name changes, and I think one has been removed since it was written, but for the most part it's still good.

    On your repeating alerts…

    The first one looks like an alert that a .exe or .dll file is being downloaded from the internet. I can see why that would be a common one. Probably safe to suppress or disable this rule, depending on your preference, unless your users shouldn't be downloading executable binary files to their computers.

    The second one looks like an alert that a potentially suspicious .pw domain is being looked up using DNS. You might want to check the host(s) that the alert is showing up for to make sure there isn't any malicious software on it/them. Of course, if your hosts regularly access systems that are legitimate in the .pw TLD, then you might want to suppress or disable this one.

    The third is a rather common one regarding a space character in an HTTP URL that isn't being formatted with an escape sequence (i.e. %20), which should be done to adhere to proper specs, but sometimes isn't. This one should be safe to suppress or disable.

    Edit to add: Your second alert could also be caused by a torrent client, connecting to a user in the country that uses the .pw TLD for data.



  • Hey you were right. It was because of bittorrent. It was blocking all traffic to .PW

    I turned that rule off.



  • the google block in snort beacuse (portscan) TCP Portscan
    i must whats do?
    Portscan Detection
    protocol tcp
    scan type all
    Sensitivity low



  • I have setup snort and it's been running well.  Thank you for those here with the setup tips.

    Today I tried to download FireFox and it all timed out to address: download-installer.cdn.mozilla.net

    I've followed the setup and disabled the ET-Policy-Mozilla rule.  What else could be affecting this?  I've done a few searches and haven't found anything here or elsewhere.



  • @Fobio:

    I have setup snort and it's been running well.  Thank you for those here with the setup tips.

    Today I tried to download FireFox and it all timed out to address: download-installer.cdn.mozilla.net

    I've followed the setup and disabled the ET-Policy-Mozilla rule.  What else could be affecting this?  I've done a few searches and haven't found anything here or elsewhere.

    Normally the alerts tab for the interface should give a clue, does it say anything?



  • @Mr.:

    @Fobio:

    I have setup snort and it's been running well.  Thank you for those here with the setup tips.

    Today I tried to download FireFox and it all timed out to address: download-installer.cdn.mozilla.net

    I've followed the setup and disabled the ET-Policy-Mozilla rule.  What else could be affecting this?  I've done a few searches and haven't found anything here or elsewhere.

    Normally the alerts tab for the interface should give a clue, does it say anything?

    Likely this:

    1:2003492 ET MALWARE Suspicious Mozilla User-Agent - Likely Fake (Mozilla/4.0)



  • Hey guys,

    I keep getting the following alert "2000419 ET POLICY PE EXE or DLL Windows file download" but I dot even have emerging-policy.rules enabled (I never have)….. I only have
    emerging-botcc.rules
    emerging-compromised.rules
    emerging-dshield.rules
    emerging-exploit.rules
    emerging-malware.rules
    emerging-trojan.rules
    emerging-worm.rules

    Is it possible that it's coming from one of these other categories?

    I've force disabled it for now, but I have no idea why it's showing up...



  • @jflsakfja:

    The Missing Part to Quick Snort Setup Instructions for New Users

    Instructions on making the most of your shiny new IDS
    Snort is designed to block pretty much anything you can think of. That's why there are many false positives. When I first started using snort, I was constantly banging my head on my desk because most sites would be blocked for (seemingly) no reason.
    The CORRECT way to stop false positives is to disable the rules causing them, NOT using suppression lists. I may hear you ask "but all other places on the internet say use suppression lists, why shouldn't I?".
    A little (simplified) info on how snort works will help you understand why.
    Snort takes the packets and analyses them. Matches to the rules will be forwarded to alerts, then pfsense's plugin takes over and bans them. Suppression lists work just before the last step. They stop alerts from being produced. Disabling rules stops the "process" at the very beginning. Why analyze a packet if you are going to ignore it? This saves CPU processing which could be used for other purposes (eg enable more rules).
    There are times when this will not work. Rules deep deep inside snort (preprocessor rules) have no way of being disabled (if I'm wrong about this, please correct me). That's where suppression lists become useful.

    With that out of the way, this is the process to stop false positives.

    1. Identify the rule causing them. On the alerts tab you will find all alerts (no kidding). The last columns should show a number in the format x:YYYY:x and an explanation for the rule.
      I'll use this for this example:
      x:2000419:x ET POLICY PE EXE or DLL Windows file download
    2. copy the YYYY part (2000419). Take a look at the explanation. ET (emerging threats) POLICY. This means you'll find this rule in emerging-policy list.
    3. go to the snort home page (services> snort). Click the e to edit interface settings, then go to rules. In the drop down select emerging-policy. Assuming you use firefox, CTRL+F and paste the rule number (called sig_id, signature ID) and click next. For other browsers, find a way to search the page for a term and enter the number there.
    4. click the red or yellow (depending if you previously enabled the rule) to turn it into a lighter shade of yellow (see bottom of page).
    5. top of page, click apply changes and wait for the page to reload.
    6. go back to the snort home page and restart the interface (click the red x until it becomes green, wait a couple of seconds and click it again to turn it back to red) <<< DO NOT FORGET THIS STEP
      –----warning!!!-------
      as of version 2.5.8 the icons are now swapped. Green is running, red is not running. So invert the colors above

    1. relax, the rule is now disabled and will stop generating alerts. Go to blocked tab, and find the ip that it previously banned and unban it (click the button to the right of the explanation).

    In that rare case you cannot find the rule causing the alert (eg explanation does not offer information about the list), first check GPLv2 list, then IPS policy list. If you still cannot find it, a suppression entry is needed. Simply click the add to suppression list (little +) next to the rule on the alerts tab. Assuming you have set up your suppression list correctly, it will be added to it. Restart the interface (step 6 above), unban the ip, and you are done!

    And now for my contribution to the community. The default enabled rules are too relaxed. We need to enable more rules, but a word of caution. ONLY USE THIS LIST IF YOU HAVE ENOUGH MEMORY.
    I'm currently using it on redundant CARP firewalls, with a crappy p4 cpu and 2GB of ram each. The systems average about 25-30% RAM usage.The list below shows how snort is configured on a production environment and works perfectly (for me) but it is not complete. Entries that do not have a DONE > in front of them are NOT COMPLETED. Please review and make changes depending on your environment.

    In tab "Rules", under "Category" select:
    (--- means blank table at time of writing)

    DONE > emerging-activex > all

    DONE > emerging-attack_responses > all

    DONE > emerging-botcc > all

    DONE > emerging-chat > all except:
    2010784 ET CHAT Facebook Chat (send message)
    2010785 ET CHAT Facebook Chat (buddy list)
    2010786 ET CHAT Facebook Chat (settings)
    2010819 ET CHAT Facebook Chat using XMPP
    2002327 ET CHAT Google Talk (Jabber) Client Login
    2002334 ET CHAT Google IM traffic Jabber client sign-on
    2001241 ET CHAT MSN file transfer request
    2001242 ET CHAT MSN file transfer accept
    2001243 ET CHAT MSN file transfer reject
    2001682 ET CHAT MSN IM Poll via HTTP
    2002192 ET CHAT MSN status change
    2008289 ET CHAT Possible MSN Messenger File Transfer
    2009375 ET CHAT General MSN Chat Activity
    2009376 ET CHAT MSN User-Agent Activity

    DONE > emerging-ciarmy > all

    DONE > emerging-compromised > all

    DONE > emerging-current_events > all

    DONE > emerging-deleted > ---

    DONE > emerging-dns > all except:
    2008446 ET DNS Excessive DNS Responses with 1 or more RR's (100+ in 10
    seconds) - possible Cache Poisoning Attempt
    2008470 ET DNS Excessive NXDOMAIN responses - Possible DNS Backscatter or Domain Generation Algorithm Lookups
    2001117 ET DNS Standard query response, Name Error

    DONE > emerging-dos > all

    DONE > emerging-drop > all

    DONE > emerging-dshield > all

    DONE > emerging-exploit > all except:
    2001058 ET EXPLOIT libpng tRNS overflow attempt
    2002913 ET EXPLOIT VNC Client response
    2002914 ET EXPLOIT VNC Server VNC Auth Offer
    2002919 ET EXPLOIT VNC Good Authentication Reply
    2002915 ET EXPLOIT VNC Authentication Reply
    2002758 ET EXPLOIT WMF Escape Record Exploit - Version 1
    2002742 ET EXPLOIT WMF Escape Record Exploit - Version 3

    DONE > emerging-ftp > all

    DONE > emerging-games > all

    DONE > emerging-icmp > ---

    DONE > emerging-icmp_info > ---

    DONE > emerging-imap > ---

    DONE > emerging-inappropriate > all except:
    2002925 ET INAPPROPRIATE Google Image Search, Safe Mode Off
    2001608 ET INAPPROPRIATE Likely Porn

    DONE > emerging-info > all except:
    2014472 ET INFO JAVA - Java Archive Download
    2014473 ET INFO JAVA - Java Archive Download By Vulnerable Client
    2014819 ET INFO Packed Executable Download
    2015016 ET INFO FTP STOR to External Network
    2015561 ET INFO PDF Using CCITTFax Filter
    2015744 ET INFO EXE IsDebuggerPresent (Used in Malware Anti-Debugging)
    2016360 ET INFO JAVA - ClassID
    2016361 ET INFO JAVA - ClassID
    2016404 ET INFO MPEG Download Over HTTP (1)

    DONE > emerging-malware > all except:
    2008438 ET MALWARE Possible Windows executable sent when remote host claims to send a Text File

    DONE > emerging-misc > all

    DONE > emerging-mobile_malware > all except:
    2012251 ET MOBILE_MALWARE Google Android Device HTTP Request
    2012848 ET MOBILE_MALWARE Possible Mobile Malware POST of IMEI International Mobile Equipment Identity in URI

    DONE > emerging-netbios > all

    DONE > emerging-p2p > all except:
    2000369 ET P2P BitTorrent Announce
    2007727 ET P2P possible torrent download
    2008581 ET P2P BitTorrent DHT ping request
    2008583 ET P2P BitTorrent DHT nodes reply
    2008585 ET P2P BitTorrent DHT announce_peers request
    2010144 ET P2P Vuze BT UDP Connection (5)
    2011699 ET P2P Bittorrent P2P Client User-Agent (Transmission/1.x)

    *emerging-policy > all except:
    2000419 ET POLICY PE EXE or DLL Windows file download
    2000428 ET POLICY ZIP file download
    2001115 ET POLICY MSI (microsoft installer file) download
    2003595 ET POLICY exe download via HTTP - Informational
    2001898 ET POLICY eBay Bid Placed
    2001907 ET POLICY eBay Placing Item for sale
    2001908 ET POLICY eBay View Item
    2001909 ET POLICY eBay Watch This Item
    2003303 ET POLICY FTP Login Attempt (non-anonymous)
    2003410 ET POLICY FTP Login Successful
    2003121 ET POLICY docs.google.com Activity
    2003597 ET POLICY Google Calendar in Use
    2002801 ET POLICY Google Desktop User-Agent Detected
    2002838 ET POLICY Google Search Appliance browsing the Internet
    2000035 ET POLICY Hotmail Inbox Access
    2000036 ET POLICY Hotmail Message Access
    2000037 ET POLICY Hotmail Compose Message Access
    2000038 ET POLICY Hotmail Compose Message Submit
    2000039 ET POLICY Hotmail Compose Message Submit Data
    2008238 ET POLICY Hotmail Inbox Access
    2008239 ET POLICY Hotmail Message Access
    2008240 ET POLICY Hotmail Compose Message Access
    2008242 ET POLICY Hotmail Access Full Mode
    2006408 ET POLICY HTTP Request on Unusual Port Possibly Hostile
    2006409 ET POLICY HTTP POST on unusual Port Possibly Hostile
    2002330 ET POLICY Google Talk TLS Client Traffic
    2002332 ET POLICY Google IM traffic Windows client user sign-on
    2002333 ET POLICY Google IM traffic friend invited
    2002878 ET POLICY iTunes User Agent
    2002722 ET POLICY MP3 File Transfer Outbound
    2002723 ET POLICY MP3 File Transfer Inbound
    2001114 ET POLICY Mozilla XPI install files download
    2001973 ET POLICY SSH Server Banner Detected on Expected Port
    2001974 ET POLICY SSH Client Banner Detected on Expected Port
    2001975 ET POLICY SSHv2 Server KEX Detected on Expected Port
    2001976 ET POLICY SSHv2 Client KEX Detected on Expected Port
    2001977 ET POLICY SSHv2 Client New Keys detected on Expected Port
    2001978 ET POLICY SSH session in progress on Expected Port
    2001979 ET POLICY SSH Server Banner Detected on Unusual Port
    2001980 ET POLICY SSH Client Banner Detected on Unusual Port
    2001981 ET POLICY SSHv2 Server KEX Detected on Unusual Port
    2001982 ET POLICY SSHv2 Client KEX Detected on Unusual Port
    2001983 ET POLICY SSHv2 Client New Keys Detected on Unusual Port
    2001984 ET POLICY SSH session in progress on Unusual Port
    2013031 ET POLICY Python-urllib/ Suspicious User Agent
    2013414 ET POLICY Executable served from Amazon S3
    2014297 ET POLICY Vulnerable Java Version 1.7.x Detected
    2012647 ET POLICY Dropbox.com Offsite File Backup in Use
    2012648 ET POLICY Dropbox Client Broadcasting
    2014313 ET POLICY Executable Download From DropBox

    DONE > emerging-pop3 > ---

    DONE > emerging-rbn-malvertisers > all

    DONE > emerging-rbn > all

    DONE > emerging-rpc > ---

    DONE > emerging-scada > all

    DONE > emerging-scan > all except
    2002992 ET SCAN Rapid POP3 Connections - Possible Brute Force Attack
    2002993 ET SCAN Rapid POP3S Connections - Possible Brute Force Attack
    2002994 ET SCAN Rapid IMAP Connections - Possible Brute Force Attack
    2002995 ET SCAN Rapid IMAPS Connections - Possible Brute Force Attack

    DONE > emerging-shellcode > all except
    2011803 ET SHELLCODE Possible TCP x86 JMP to CALL Shellcode Detected
    2012252 ET SHELLCODE Common 0a0a0a0a Heap Spray String
    2012257 ET SHELLCODE Common %0c%0c%0c%0c Heap Spray String
    2012510 ET SHELLCODE UTF-8/16 Encoded Shellcode
    2013222 ET SHELLCODE Excessive Use of HeapLib Objects Likely Malicious Heap Spray Attempt
    2013267 ET SHELLCODE Hex Obfuscated JavaScript Heap Spray 0a0a0a0a

    DONE > emerging-smtp > all

    DONE > emerging-snmp > all

    DONE > emerging-sql > all

    DONE > emerging-telnet > all

    DONE > emerging-tftp > all

    DONE > emerging-tor > all

    emerging-trojan > all except

    DONE > emerging-user_agents > all except:
    2010697 ET USER_AGENTS Suspicious User-Agent Beginning with digits - Likely spyware/trojan

    DONE > emerging-voip > all

    DONE > emerging-web_client > all except
    2011347 ET WEB_CLIENT Possible String.FromCharCode Javascript Obfuscation Attempt
    2011507 ET WEB_CLIENT PDF With Embedded File
    2010518 ET WEB_CLIENT Possible HTTP 404 XSS Attempt (External Source)
    2012119 ET WEB_CLIENT Possible Hex Obfuscation Usage On Webpage
    2012205 ET WEB_CLIENT Possible Malicious String.fromCharCode with charCodeAt String
    2012266 ET WEB_CLIENT Hex Obfuscation of unescape % Encoding
    2012272 ET WEB_CLIENT Hex Obfuscation of eval % Encoding
    2012398 ET WEB_CLIENT Hex Obfuscation of replace Javascript Function % Encoding

    DONE > emerging-web_server > all except
    2003099 ET WEB_SERVER Poison Null Byte

    emerging-web_specific_apps > all except:
    2010890 ET WEB_SPECIFIC_APPS phpBB3 registration (Step1 GET)
    2010891 ET WEB_SPECIFIC_APPS phpBB3 registration (Step2 POST)
    2010892 ET WEB_SPECIFIC_APPS phpBB3 registration (Step3 GET)
    2010893 ET WEB_SPECIFIC_APPS phpBB3 registration (Step4 POST)

    DONE > emerging-worm > all

    DONE > GPLv2 community rules > all except
    254 DNS SPOOF query response with TTL of 1 min. and no authority
    384 PROTOCOL-ICMP PING
    385 PROTOCOL-ICMP traceroute
    399 PROTOCOL-ICMP Destination Unreachable Host Unreachable
    402 PROTOCOL-ICMP Destination Unreachable Port Unreachable
    408 PROTOCOL-ICMP Echo Reply
    540 POLICY-SOCIAL Microsoft MSN message
    648 INDICATOR-SHELLCODE x86 NOOP
    649 INDICATOR-SHELLCODE x86 setgid 0
    1200 INDICATOR-COMPROMISE Invalid URL
    1201 INDICATOR-COMPROMISE 403 Forbidden
    1292 INDICATOR-COMPROMISE directory listing
    1390 INDICATOR-SHELLCODE x86 inc ebx NOOP
    1394 INDICATOR-SHELLCODE x86 inc ecx NOOP
    1437 FILE-IDENTIFY Microsoft Windows Media download detected
    1841 FILE-OTHER Oracle Javascript URL host spoofing attempt
    1846 POLICY-MULTIMEDIA vncviewer Java applet download attempt
    1852 SERVER-WEBAPP robots.txt access
    1986 POLICY-SOCIAL Microsoft MSN outbound file transfer request
    1988 POLICY-SOCIAL Microsoft MSN outbound file transfer accept
    1989 POLICY-SOCIAL Microsoft MSN outbound file transfer rejected
    1990 POLICY-SOCIAL Microsoft MSN user search
    1991 POLICY-SOCIAL Microsoft MSN login attempt
    2180 PUA-P2P BitTorrent announce request
    2181 PUA-P2P BitTorrent transfer
    2707 FILE-IMAGE JPEG parser multipacket heap overflow
    3463 SERVER-WEBAPP awstats access
    25518 OS-OTHER Apple iPod User-Agent detected
    25519 OS-OTHER Apple iPad User-Agent detected
    25520 OS-OTHER Apple iPhone User-Agent detected
    25521 OS-OTHER Android User-Agent detected
    25522 OS-OTHER Nokia User-Agent detected
    25523 OS-OTHER Samsung User-Agent detected
    25524 OS-OTHER Kindle User-Agent detected
    25525 OS-OTHER Nintendo User-Agent detected

    *IPS Policy - Security > all except
    4152 BROWSER-PLUGINS Microsoft Windows Media Player 6.4 ActiveX object access
    19436 BROWSER-IE Microsoft Internet Explorer CStyleSheetRule array memory corruption attempt

    Suppression List:
    #GLOBAL

    gen_id 1

    suppress gen_id 1, sig_id 536
    suppress gen_id 1, sig_id 648
    suppress gen_id 1, sig_id 653
    suppress gen_id 1, sig_id 1390
    suppress gen_id 1, sig_id 2452
    suppress gen_id 1, sig_id 11192
    suppress gen_id 1, sig_id 15306
    suppress gen_id 1, sig_id 16313
    suppress gen_id 1, sig_id 17458
    suppress gen_id 1, sig_id 20583
    suppress gen_id 1, sig_id 23098
    suppress gen_id 1, sig_id 2000334
    suppress gen_id 1, sig_id 2008120
    suppress gen_id 1, sig_id 2010516
    suppress gen_id 1, sig_id 20122758
    suppress gen_id 1, sig_id 2014518
    suppress gen_id 1, sig_id 2014520
    suppress gen_id 1, sig_id 2100366
    suppress gen_id 1, sig_id 2100368
    suppress gen_id 1, sig_id 2100651
    suppress gen_id 1, sig_id 2101390
    suppress gen_id 1, sig_id 2101424
    suppress gen_id 1, sig_id 2102314
    suppress gen_id 1, sig_id 2103134
    suppress gen_id 1, sig_id 2500056
    suppress gen_id 1, sig_id 100000230
    suppress gen_id 3, sig_id 14772
    #(http_inspect) DOUBLE DECODING ATTACK
    suppress gen_id 119, sig_id 2
    #(http_inspect) BARE BYTE UNICODE ENCODING
    suppress gen_id 119, sig_id 4
    #(http_inspect) IIS UNICODE CODEPOINT ENCODING
    suppress gen_id 119, sig_id 7
    #(http_inspect) NON-RFC DEFINED CHAR [**]
    suppress gen_id 119, sig_id 14
    #(http_inspect) UNKNOWN METHOD
    suppress gen_id 119, sig_id 31
    #(http_inspect) SIMPLE REQUEST
    suppress gen_id 119, sig_id 32
    #(http_inspect) NO CONTENT-LENGTH OR TRANSFER-ENCODING IN HTTP RESPONSE
    suppress gen_id 120, sig_id 2
    #(http_inspect) NO CONTENT-LENGTH OR TRANSFER-ENCODING IN HTTP RESPONSE
    suppress gen_id 120, sig_id 3
    #(http_inspect) HTTP RESPONSE HAS UTF CHARSET WHICH FAILED TO NORMALIZE
    suppress gen_id 120, sig_id 4
    #(http_inspect) HTTP RESPONSE GZIP DECOMPRESSION FAILED
    suppress gen_id 120, sig_id 6
    #(http_inspect) INVALID CONTENT-LENGTH OR CHUNK SIZE
    suppress gen_id 120, sig_id 8
    #(http_inspect) JAVASCRIPT OBFUSCATION LEVELS EXCEEDS 1
    suppress gen_id 120, sig_id 9

    Unknown

    suppress gen_id 120, sig_id 10
    #(smtp) Attempted response buffer overflow: 1448 chars
    suppress gen_id 124, sig_id 3
    #(ftp_telnet) Invalid FTP Command
    suppress gen_id 125, sig_id 2
    #(ssp_ssl) Invalid Client HELLO after Server HELLO Detected
    suppress gen_id 137, sig_id 1
    #(IMAP) Unknown IMAP4 command
    suppress gen_id 141, sig_id 1

    I did the above and I'm getting this error in my System Logs and Snort isn't starting:

    FATAL ERROR: /usr/local/etc/snort/snort_63694_igb0/rules/snort.rules(5021) byte_test rule option cannot extract more than 4 bytes without valid string prefix.



  • @djseto:

    I did the above and I'm getting this error in my System Logs and Snort isn't starting:

    FATAL ERROR: /usr/local/etc/snort/snort_63694_igb0/rules/snort.rules(5021) byte_test rule option cannot extract more than 4 bytes without valid string prefix.

    Have you searched this sub-forum using the error message text?  If you do, you should encounter this recent thread with your answer:
    https://forum.pfsense.org/index.php?topic=130993.msg722272#msg722272.

    Bill



  • OP, thank you for providing this guide.

    I have some questions.

    @bmeeks:

    16.  Click the Preprocessors tab.

    17.  Scroll down into the General Preprocessor Settings area and then check (or enable) all of the preprocessors listed in that section EXCEPT the Sensitive Data preprocessor.  It can cause a lot of alerts and is best used after you gain some experience with Snort.

    It's not clear which section of preprocessors you are talking about. There is no General Preprocessor Settings area.

    @bmeeks:

    19.  Now click on the Categories tab.  This is where we will choose a threat detection policy and associated rules.

    20.  If you followed my advice for Snort VRT rules, this page is easy.  Just click the check box for "Use IPS Policy" and then select "Connectivity" in the drop-down.  Click Save and you're done!  Once you gain some experience with Snort, you can come back and choose one of the other two more restrictive policies.  I personally run "Balanced", but it will require some tuning if run in blocking mode.

    What is the difference between Connectivity and Balanced. The description does not explain the difference.

    Connectivity blocks most major threats with few or no false positives. Balanced is a good starter policy.
    It is speedy, has good base coverage level, and covers most threats of the day. It includes all rules in Connectivity.



  • @bimmerdriver:

    OP, thank you for providing this guide.

    I have some questions.

    @bmeeks:

    16.  Click the Preprocessors tab.

    17.  Scroll down into the General Preprocessor Settings area and then check (or enable) all of the preprocessors listed in that section EXCEPT the Sensitive Data preprocessor.  It can cause a lot of alerts and is best used after you gain some experience with Snort.

    It's not clear which section of preprocessors you are talking about. There is no General Preprocessor Settings area.

    @bmeeks:

    19.  Now click on the Categories tab.  This is where we will choose a threat detection policy and associated rules.

    20.  If you followed my advice for Snort VRT rules, this page is easy.  Just click the check box for "Use IPS Policy" and then select "Connectivity" in the drop-down.  Click Save and you're done!  Once you gain some experience with Snort, you can come back and choose one of the other two more restrictive policies.  I personally run "Balanced", but it will require some tuning if run in blocking mode.

    What is the difference between Connectivity and Balanced. The description does not explain the difference.

    Connectivity blocks most major threats with few or no false positives. Balanced is a good starter policy.
    It is speedy, has good base coverage level, and covers most threats of the day. It includes all rules in Connectivity.

    First: what bimmer do you drive? I have an E39, and a F01  :) Which one do you have? Engine? Automatic gear or manual? Color? Most important Options? In Bimmer world, we are One Big Family  :-*

    1. The General Preprocessor Settings indeed is gone. My guess is it is now 'Basic configuration settings', and a lot of other settings that used to be in 'General settings'. I think you could accept the defaults. 'Sensititive data' is now a separate setting all together: unflag it.
    2. "Connectivity" versus "balanced" is described: one is more restrictive than the other. It is really nothing more than this: in one setting more categories and rules are enabled than in the other, by default. If you wish to know which ones, enable one settings, and then inspect the rules-tab to find out. It is just a helpful default suggestion from Bill, nothing more. He didn't write a tutorial for stuff you can easily see yourself by simply enabling the setting  ;)



  • @Mr.:

    First: what bimmer do you drive? I have an E39, and a F01  :) Which one do you have? Engine? Automatic gear or manual? Color? Most important Options? In Bimmer world, we are One Big Family  :-*

    I drive an E46, specifically 2002 M3 MT coupe with a lot of mods. Using your family analogy, your F01 is the stately father and my E46 is the kid that gets into a lot of trouble. E39 and F01 is an interesting combo. What are their year / model? An E39 M5 would be a nice alternate to an F01.

    @Mr.:

    1. The General Preprocessor Settings indeed is gone. My guess is it is now 'Basic configuration settings', and a lot of other settings that used to be in 'General settings'. I think you could accept the defaults. 'Sensititive data' is now a separate setting all together: unflag it.
    2. "Connectivity" versus "balanced" is described: one is more restrictive than the other. It is really nothing more than this: in one setting more categories and rules are enabled than in the other, by default. If you wish to know which ones, enable one settings, and then inspect the rules-tab to find out. It is just a helpful default suggestion from Bill, nothing more. He didn't write a tutorial for stuff you can easily see yourself by simply enabling the setting  ;)

    Okay, that's what I thought.



  • @bmeeks:

    8.  Click the Snort Interfaces tab and then click the plus "+" icon to add a Snort interface.

    9.  On the If Settings tab, click the Enable checkbox.

    10.  In the drop-down, choose the interface.  The WAN interface is the default and is a good first choice.

    11.  In the Description textbox, enter a name (WAN again, is fine here).

    I have several OpenVPN clients that run as interfaces. Should I add them also in Snort interfaces or is it enough with just WAN?

    Thanks for this great post. I followed your post and also watched this tutorial https://youtu.be/-GgqYq5-EBg

    Thanks again!



  • New to Snort I follow this one https://www.youtube.com/watch?v=-GgqYq5-EBg&feature=youtu.be and setup accordingly only one interface eg the WAN.
    Strange enough I only see one source ip address (LAN) in the Alerts tab. I have 10 subnets, with many users using the internet, what am I overlooking?

    For instance in PFBlockerNG-develop I am see enough of the IP's of the subnets.

    Cheers Qinn



  • @qinn said in Quick Snort Setup Instructions for New Users:

    New to Snort I follow this one https://www.youtube.com/watch?v=-GgqYq5-EBg&feature=youtu.be and setup accordingly only one interface eg the WAN.
    Strange enough I only see one source ip address (LAN) in the Alerts tab. I have 10 subnets, with many users using the internet, what am I overlooking?

    For instance in PFBlockerNG-develop I am see enough of the IP's of the subnets.

    Cheers Qinn

    When you run Snort on the WAN, it sees inbound traffic from the Internet before the NAT rules are unwound. So every packet has the public WAN IP address of your firewall as the destination. Only after NAT is unwound will the actual LAN IP address be present.

    For this reason I recommend users run Snort on the LAN and not the WAN. When you run it on the LAN, it sees packets after NAT has been unwound so the IP addresses map directly to your LAN hosts.



  • @bmeeks first thank you for the advice. I have changed it from WAN to WLAN (a private VLAN subnet for an AP) which has internet access and roughly 20 nodes, smartphones, desktops, Sonos etc.
    In 2 hours time there were 10 alerts => (http_inspect) NO CONTENT-LENGTH OR TRANSFER-ENCODING IN HTTP RESPONSE

    I have only enabled "Snort will use rules from one of three pre-defined IPS policies in the Snort Subscriber rules" and IPS Policy Selection checked.



  • @qinn said in Quick Snort Setup Instructions for New Users:

    @bmeeks first thank you for the advice. I have changed it from WAN to WLAN (a private VLAN subnet for an AP) which has internet access and roughly 20 nodes, smartphones, desktops, Sonos etc.
    In 2 hours time there were 10 alerts => (http_inspect) NO CONTENT-LENGTH OR TRANSFER-ENCODING IN HTTP RESPONSE

    I have only enabled "Snort will use rules from one of three pre-defined IPS policies in the Snort Subscriber rules" and IPS Policy Selection checked.

    The HTTP_INSPECT preprocessor rules will fire frequently and these days are mostly false positives. Most admins disable several of the HTTP_INSPECT rules. Search the IDS/IPS sub-forum here for suggestions on Snort Suppression Lists to find rules that most users suggest either suppressing or disabling.



  • @bmeeks now I reread my reply, I realize I wasn't clear, I should have emphasized that I only had these ten alerts in 2 hours and that seems rather meager. I would have expected to see loads of alerts, as approximately 20 users (smartphones, desktops, Sonos etc.) are on this subnet.



  • @qinn, it depends totally on which precise rules are enabled and what the traffic on your network actually consists of. The goal in IDS/IPS is to get no or very few alerts and blocks. That means your network is relatively secure and clients are following the rules ... ☺ .

    I don't mean that to say you should never get alerts, though. Just that you don't want to be receiving hundreds per hour. Once blocking is enabled that might drive you crazy as an admin. Within the IPS Polices, the Snort team has selected rules that provide security without a ton of false positive alerts.


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