AEAD Decrypt error: cipher final failed - after 2.6.0 to 2.7.2 Update

fholzer

I had a "weird" problem today with OpenVPN / S2S (/30 separated).
Maybe I ran into a bug...

Updated the main pfSense from 2.6.0 to 2.7.2.
4 sites also to from 2.6.0 to 2.7.2.
1 site was still running on 2.6.0.

The 2.7.2 sites all had the error: "AEAD Decrypt error: cipher final failed" after the update.
The 2.6.0 site was still up and running → no errors.

So I checked the ciphers and the configuration ... in the past it was old ciphers or a "weird" combination/fallback.

Adjusted a lot, tried a lot:

Different TLS Key Usage Mode, TLS Keydir directions, ...
Different Data Encryption Algorithms, None Fallback, other Fallback,
Different Auth digest algorithm from SHA-1 to SHA384, ...
Different Custom Options from setenv disable-dco 1, over mtu settings, mssfix, ...

The interesting part → I changed these settings on the 2.7.2 server, the 2.7.2 client side, and on the 2.6.0 client side (just to make sure - since it should work on both, the old and new versions).

The 2.6.0 client always worked with every cipher/combination I tried. (which should work in my brain)
The 2.7.2 client never worked. Always the "AEAD Decrypt error: cipher final failed" error.

a small log:

Mar 3 16:39:21	openvpn	47146	Control Channel: TLSv1.3, cipher TLSv1.3 TLS_AES_256_GCM_SHA384, peer certificate: 2048 bits RSA, signature: RSA-SHA256, peer temporary key: 253 bits X25519
Mar 3 16:39:21	openvpn	47146	[vpn.xxxx.xx] Peer Connection Initiated with [AF_INET]xx.83.xx.206:1194
Mar 3 16:39:21	openvpn	47146	TLS: move_session: dest=TM_ACTIVE src=TM_INITIAL reinit_src=1
Mar 3 16:39:21	openvpn	47146	TLS: tls_multi_process: initial untrusted session promoted to trusted
Mar 3 16:39:22	openvpn	47146	Data Channel MTU parms [ mss_fix:1403 max_frag:0 tun_mtu:1500 tun_max_mtu:1600 headroom:136 payload:1768 tailroom:562 ET:0 ]
Mar 3 16:39:22	openvpn	47146	Outgoing Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key
Mar 3 16:39:22	openvpn	47146	Incoming Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key
Mar 3 16:39:22	openvpn	47146	Initialization Sequence Completed
Mar 3 16:39:22	openvpn	47146	Data Channel: cipher 'AES-256-GCM'
Mar 3 16:39:22	openvpn	47146	Timers: ping 10, ping-restart 60
Mar 3 16:39:31	openvpn	47146	AEAD Decrypt error: cipher final failed

the "solution":

So in the end i added a pull in the "Custom options" Field (cause i thought ... why not ...) and the 2.7.2 client started to work again.
No error in the logs, i can reach the remote site again.

removing the pull -> error is back.

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If the openvpn is in client mode, shouldn't it use pull on its own?!