Possible to disable SSH CBC cipher and weak MAC hashing?

[boss82]

Hi,

May I check if it is possible to disable SSH CBC cipher and weak MAC hashing on Palo Alto Firewall?

If so, may I know how to do it.

Had no luck searching for a solution online.

Seems like there is no menu/config file (e.g. /etc/ssh/ssh_config) to edit such settings.

This is with relation to Nessus vulnerability findings.

Try to see how it can be addressed.

https://www.tenable.com/plugins/index.php?view=single&id=70658

https://www.tenable.com/plugins/index.php?view=single&id=71049

Thank you in advance

[mmmccorkle]

Hey,

Even the latest Pan-OS version running in FIPS mode still has cbc enabled. There is not a way to modify this. 

Non-FIPS/CC mode 

Decryption (SSHv2 only) 

Ciphers: aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,aes192-cbc,aes256-cbc 

MAC Algorithms: hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 

aes192-ctr

aes256-ctr

aes128-gcm

aes256-gcm

FIPS/CC mode 

HMAC – HMAC-SHA-1 

Authentication – RSA (2048 bit key only) 

Key agreement – DH Group 14 (2048 bit) 

Symmetric Algorithm – AES128, AES192, or AES256 (CBC or CTR for all three) 

[Dave_Fitzjarrell]

Good link for setting ciphers.  Remember do not include CBC in your config.

https://docs.paloaltonetworks.com/pan-os/9-0/pan-os-cli-quick-start/get-started-with-the-cli/refresh...

For MAC's I used these:

configure
set deviceconfig system ssh mac mgmt hmac-sha1
set deviceconfig system ssh mac mgmt hmac-sha2-256
set deviceconfig system ssh mac mgmt hmac-sha2-512
commit

[KirubaKaran]

Hi Team,

                  As per below I could understand the CBC mode cipher encryption was handling by server not firewall right ? correct me If I'm wrong ...... Also for that we need to reach the concern server OS vendor or support to change encryption CBC to CTR, GCM encryption.

 IBM SERVER

https://www.ibm.com/support/pages/disabling-cipher-block-chaining-cbc-mode-ciphers-and-weak-mac-algo...

PA-Community-post

https://live.paloaltonetworks.com/t5/general-topics/ssh-ssl-issues-reported-from-vulnerability-asses...

Regards

Kirubakaran.M