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Ianvdl | 1 year ago

> Statement

> The flaw affects RHEL9 as the regression was introduced after the OpenSSH version shipped with RHEL8 was published.

discuss

order

chasil|1 year ago

However, we see the -D option on the listening parent:

  $ ps ax | grep sshd | head -1
     1306 ?        Ss     0:01 sshd: /usr/sbin/sshd -D [listener] 0 of 10-100 startups
As mentioned elsewhere here, is -D sufficient to avoid exploitation, or is -e necessary as well?

  $ man sshd | sed -n '/ -[De]/,/^$/p'
     -D      When this option is specified, sshd will not
             detach and does not become a daemon.  This
             allows easy monitoring of sshd.

     -e      Write debug logs to standard error instead
             of the system log.
RHEL9 is also 64-bit only, and we see from the notice:

"we have started to work on an amd64 exploit, which is much harder because of the stronger ASLR."

On top of writing the exploit to target 32-bit environments, this also requires a DSA key that implements multiple calls to free().

There is a section on "Rocky Linux 9" near the end of the linked advisory where unsuccessful exploit attempts are discussed.

Arnavion|1 year ago

>As mentioned elsewhere here, is -D sufficient to avoid exploitation, or is -e necessary as well?

https://github.com/openssh/openssh-portable/blob/V_9_8_P1/ss...

sshd.c handles no_daemon (-D) and log_stderr (-e) independently. log_stderr is what is given to log_init in log.c that gates the call to syslog functions. There is a special case to set log_stderr to true if debug_flag (-d) is set, but nothing for no_daemon.

I can't test it right now though so I may be missing something.