Suricata hash matching Please Help

bmeeks

I have an idea what may be wrong, but testing the fix will require you to be familiar with using vi or a similar editor in a CLI session on the firewall.

If you are comfortable making an edit to a file for testing, here are the steps:

1. Make a copy of the original file for safekeeping


cp /usr/local/pkg/suricata/suricata_generate_yaml.php /usr/local/pkg/suricata/suricata_generate_yaml.php.orig

2. Now open /usr/local/pkg/suricata/suricata_generate_yaml.php in vi or a similar editor on the firewall. You can also use something like WinSCP connected to the firewall and then right-click on the file to edit it.

3. Locate line #698 in the file. It will look like this:


	$http_hosts_default_policy = "     personality: IDS\n     request-body-limit: 4096\n     response-body-limit: 4096\n";

Change it to look like this:


	$http_hosts_default_policy = "     personality: IDS\n     request-body-limit: 0\n     response-body-limit: 0\n";

Notice the 4096 values are changed to zero. This sets the HTTP session decoding to unlimited. Formerly it was limited to 4096 bytes. Be careful and don't alter the indention or position of spaces in the line! Just carefully replace "4096" with "0" in both spots.

4. Save the change to the file and then go into the Suricata GUI and open the interface for editing. You don't have to make an actual change, but just click the SAVE button at the bottom of the page to force creation of an updated suricata.yaml configuration.

5. Now on the INTERFACES tab in the GUI restart that Suricata interface and test the file extraction again. Let me know if that works.

Thanks,
Bill

steve40

Hi meeks…thanks for taking the time to respond

$http_hosts_default_policy = " personality: IDS\n request-body-limit: 0\n response-body-limit: 0\n";

I followed your instructions but still no luck

It stored the 30K in the /files directory as follows

[2.4.2-RELEASE][admin@pfSense.localdomain]/var/log/suricata/suricata_re058347/files: cat file.1676.meta
TIME: 04/12/2018-23:00:08.341864
SRC IP: 63.96.49.202
DST IP: 192.168.0.2
PROTO: 6
SRC PORT: 80
DST PORT: 63020
APP PROTO: http
HTTP URI: /sql.exe
HTTP HOST: 63.96.49.202
HTTP REFERER: http://63.96.49.202/
HTTP USER AGENT: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0
FILENAME: /sql.exe
MAGIC: PE32+ executable (GUI) x86-64, for MS Windows
STATE: TRUNCATED
SIZE: 4380

/var/log/suricata/suricata_re058347: tail -100f eve.json | grep sql.exe

I'm going to try with another executable as this one is a UPX packed exe

bmeeks

Hmm… I was hoping the change in decode limits would help. I'm afraid that was my best idea ... :(.

You might have to try posting a question over on the Suricata Redmine site here: https://redmine.openinfosecfoundation.org/projects/suricata

Bill

steve40

Thanks, Bill :)

steve40

Now I'm stuck trying to figure out how to post this question on their site?

lol :(

ivor

https://redmine.openinfosecfoundation.org/account/register

steve40

Hello Ivor.

I did register. Just not seeing a button or anything that would allow for posting

Thanks

steve40

Meeks,

One thing I noticed that's odd is that even after making the change to the php file as you indicated the suricata.yaml file in the interface subfolder keeps changing back to 4096.

If I set it manually to 0 in the .yaml file and leave suricata turned off at the pfsense level and run suricata via the **suricata -c **.yaml -s single.rulefileIconfigured.rules -i re0 from the shell it works as expected. When I restart the interface it reverts back to 4096 in the yaml file

I've tried uninstalling, reinstalling, modifying the php BEFORE creating the interface and all… no luck

I even changed the php file to 10x the original size and it simply reverted back to 4096 upon the next restart of the interface

bmeeks

Did you also check that parameter within the GUI to be sure it is set to "0"? You will find it on the APP PARSERS tab. Check that the default HTTP Engine has those two values set to zero instead of 4096. I forgot to mention that in my earlier post.

Bill

steve40

Meeks. You're the best :D

If you're ever in NY rounds on me

Thanks bro

steve40

Hi Meeks.

Im guessing this is normal behavior since suricata is merely intercepting a tcp stream and examining it but ive noticed that with the file hash comparison and blocking turned on the ips will always allow the first instance of a blacklisted file theough. After that the ips engine will block the DST address and subsequent attempts to download the same file will be blocked along with the entire host.

You know of any way to force it not to allow the first instance through?

Also. Do you know if theres a way to have the executable name included in the alerts section without having to go to the eve.json log?

Thanks

bmeeks

@steve40:

Hi Meeks.

Im guessing this is normal behavior since suricata is merely intercepting a tcp stream and examining it but ive noticed that with the file hash comparison and blocking turned on the ips will always allow the first instance of a blacklisted file theough. After that the ips engine will block the DST address and subsequent attempts to download the same file will be blocked along with the entire host.

You know of any way to force it not to allow the first instance through?

Also. Do you know if theres a way to have the executable name included in the alerts section without having to go to the eve.json log?

Thanks

What you are seeing is an artifact of the Legacy Mode blocking. Suricata, in that mode, is using libpcap to get copies of each packet traversing the interface. It examines the copy (and in many cases may need to see a number of copies of additional packets) to make a block/no-block decision. Once it decides to block, it makes a system call to insert the offender's IP address into a built-in pfSense firewall table called snort2c. That will result in subsequent traffic from that IP address getting blocked until the IP is removed from that pf table. Suricata will also optionally kill all open states associated with the IP (the default is to kill open states). However, remember I said "copies of packets", so that initial download can get started as the original packets continued on to the firewall and then the host behind it (assuming the traffic was solicited by the host in the first place). This is what we call "packet leakage" and is inherent in Legacy Mode.

To prevent this you would need to run with Inline IPS Mode, but that mode uses native Netmap functionality in FreeBSD and also requires the NIC hardware driver to fully support Netmap operation. Some do, but many to do not. Also, you must remember that Suricata needs to download the entire file in order to compute the checksum to check against the list. So a lot of memory might be required for buffering.

Bill

steve40

@bmeeks:

@steve40:

Hi Meeks.

Im guessing this is normal behavior since suricata is merely intercepting a tcp stream and examining it but ive noticed that with the file hash comparison and blocking turned on the ips will always allow the first instance of a blacklisted file theough. After that the ips engine will block the DST address and subsequent attempts to download the same file will be blocked along with the entire host.

You know of any way to force it not to allow the first instance through?

Also. Do you know if theres a way to have the executable name included in the alerts section without having to go to the eve.json log?

Thanks

What you are seeing is an artifact of the Legacy Mode blocking. Suricata, in that mode, is using libpcap to get copies of each packet traversing the interface. It examines the copy (and in many cases may need to see a number of copies of additional packets) to make a block/no-block decision. Once it decides to block, it makes a system call to insert the offender's IP address into a built-in pfSense firewall table called snort2c. That will result in subsequent traffic from that IP address getting blocked until the IP is removed from that pf table. Suricata will also optionally kill all open states associated with the IP (the default is to kill open states). However, remember I said "copies of packets", so that initial download can get started as the original packets continued on to the firewall and then the host behind it (assuming the traffic was solicited by the host in the first place). This is what we call "packet leakage" and is inherent in Legacy Mode.

To prevent this you would need to run with Inline IPS Mode, but that mode uses native Netmap functionality in FreeBSD and also requires the NIC hardware driver to fully support Netmap operation. Some do, but many to do not. Also, you must remember that Suricata needs to download the entire file in order to compute the checksum to check against the list. So a lot of memory might be required for buffering.

Bill

Hi Bill,

thanks for the reply. I had a feeling that that would be the case so I used Inline mode and saw the same behavior. I belive the interface is a realtek card based on the "re0" …

bmeeks

When using Inline IPS mode, you would have to manually change the associated rule or rules to DROP action, but I'm still not sure what the impact is with these file matching rules. As I stated earlier, it's obvious Suricata will have to let the entire file download before it can check the checksum to see if the file is on a blacklist or whitelist. So the part I'm not sure about is what Suricata is doing with the parts of the file as it is downloaded and before the checksum can be calculated. If Suricata buffered the entire file, then exactly what will it tell the LAN host that started the transfer? If that host does not get any packets during the buffering, it will assume the download is failing. If Suricata feeds it the file parts, then it can't block the download. I've never investigated this feature, though, so I really am not sure how it works.

Bill

steve40

I see where you're coming from.

Oh well, so much for trying to use suricata as a content filter lol

I wonder how clamav gets around the buffering/leaving client in limbo issue. I wrote a md5 signature for the exact same file and injected it into the .ndb files clam uses and it picked it up and blocked it on first attempt. No issues.

Only thing is, for performance reasons id rather have done the checking lower down the stack

steve40

Hiya Meeks… I got all the suricata file matching stuff working ...thanks for your help

I identify binary files and block them via an empty hash whitelist. Which basically turns the box into a carbon black operating at the gateway level. Works like a charm. (as long as you got pass rules for microsloth and places you wanna get exes from)

It all works like a charm UNTIL.....

you go to download an executable from an HTTPS enabled site.

So out of desperation I'm going to ask a stupid question

Is there a way to intercept these files while passing through an HTTPS session? I've got MITM fully working but I'm guessing that suricata operates at the NIC card and Squid decrypts the packet way higher up the stack...

I really really really don't wanna have to do virus checking via ClamAv

By the way, I've got this whole setup running on a KVM hypervisor so I can get very creative If I need to

thanks

bmeeks

@steve40:

Hiya Meeks… I got all the suricata file matching stuff working ...thanks for your help

I identify binary files and block them via an empty hash whitelist. Which basically turns the box into a carbon black operating at the gateway level. Works like a charm. (as long as you got pass rules for microsloth and places you wanna get exes from)

It all works like a charm UNTIL.....

you go to download an executable from an HTTPS enabled site.

So out of desperation I'm going to ask a stupid question

Is there a way to intercept these files while passing through an HTTPS session? I've got MITM fully working but I'm guessing that suricata operates at the NIC card and Squid decrypts the packet way higher up the stack...

I really really really don't wanna have to do virus checking via ClamAv

By the way, I've got this whole setup running on a KVM hypervisor so I can get very creative If I need to

thanks

Suricata and Snort both work at the NIC card level (more or less). When looking at the flow from the point of view of inbound traffic from the Internet, Suricata or Snort is the first thing the packet sees after leaving the NIC on the way into pfSense. Any MITM stuff is farther down the line (or higher up in the stack if you want to think from that perspective). So all Suricata is going to see is the raw HTTPS encrypted datastream.

Bill