Change weak HMAC

K80425458: Modifying the list of ciphers and MAC algorithms used by the SSH service on the BIG-IP system or BIG-IQ system

https://support.f5.com/csp/article/K80425458

SHA256 HMAC was introduced in OpenSSH 4.4/4.4p1

11.x.x uses 4.3p2: K14457: BIG-IP third-party software matrix (11.x)

If you want sha2 you need to go with 12.1.3 or 13.1.0

It does not seem hmac-sha2-256 is available on 11.6.* at all.

 rpm -qa |grep ssh-server
openssh-server-4.3p2-72.el5_6.3.0.0.3

 grep MAC /var/run/config/sshd_config
 MACS hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96

 man sshd_config
...
MACs    Specifies the available MAC (message authentication code) algorithms.  The MAC algorithm is used in protocol version 2 for data integrity pro- 
tection.  Multiple algorithms must be comma-separated.  The default is “hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96”.
...

 strings /usr/sbin/sshd |grep mac
hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
hmac-sha1
macs
%s line %d: Bad SSH2 mac spec '%s'.
%s: can not init mac %s
%s: bad mac key length: %u > %d
unsupported mac %s
no matching mac found: client %s server %s
mac_compute: no key
mac_compute: mac too long
mac %s len %d
mac_init: found %s
mac_init: unknown %s
bad mac %s [%s]
mac ok: %s [%s]
macs ok: [%s]
hmac-sha1-96
hmac-md5
hmac-md5-96
hmac-ripemd160
hmac-ripemd160@openssh.com

However, on v13.1.0.4:

 rpm -qa |grep ssh-server
openssh-server-6.6.1p1-31.el7.x86_64
openssh-server-sysvinit-6.6.1p1-31.el7.x86_64

 ssh -Q mac
hmac-sha1
hmac-sha1-96
hmac-sha2-256
hmac-sha2-512
hmac-md5
hmac-md5-96
hmac-ripemd160
hmac-ripemd160@openssh.com
umac-64@openssh.com
umac-128@openssh.com
hmac-sha1-etm@openssh.com
hmac-sha1-96-etm@openssh.com
hmac-sha2-256-etm@openssh.com
hmac-sha2-512-etm@openssh.com
hmac-md5-etm@openssh.com
hmac-md5-96-etm@openssh.com
hmac-ripemd160-etm@openssh.com
umac-64-etm@openssh.com
umac-128-etm@openssh.com

 grep MAC /var/run/config/sshd_config
MACS hmac-sha1

 man sshd_config
...
MACS hmac-sha1

     MACs    Specifies the available MAC (message authentication code) algorithms.  The MAC algorithm is used in protocol ver-
             sion 2 for data integrity protection.  Multiple algorithms must be comma-separated.  The algorithms that contain
             “-etm” calculate the MAC after encryption (encrypt-then-mac).  These are considered safer and their use recom-
             mended.  The default is:

                   hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
                   umac-64-etm@openssh.com,umac-128-etm@openssh.com,
                   hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
                   hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,
                   hmac-md5-96-etm@openssh.com,
                   hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
                   hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
                   hmac-sha1-96,hmac-md5-96
...

So you can either upgrade, or tighten up the acl for SSH access.

Hi,

did you try this out please,

tmsh modify sys sshd include "MACs "

Caution:

include

Warning: Do not use this parameter without assistance from the F5 Technical Support team. The system does not validate the commands issued using the include parameter. If you use this parameter incorrectly, you put the functionality of the system at risk.

Also happened to check on the below,

file - /var/run/config/sshd_config

 KexAlgorithms diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
 MACS hmac-md5,hmac-sha1,hmac-ripemd160,hmac-ripemd160@openssh.com,hmac-sha1-96,hmac-md5-96
 F5 - these are FIPS approved ciphers.
 Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc

You may check complete list: K13163: SSL ciphers supported on BIG-IP platforms (11.x - 13.x) https://support.f5.com/csp/article/K13163