OpenSSH 4.4 was released and mentions:
* Fix an unsafe signal hander reported by Mark Dowd. The
signal handler was vulnerable to a race condition that could
be exploited to perform a pre-authentication denial of
service. On portable OpenSSH, this vulnerability could
theoretically lead to pre-authentication remote code execution
if GSSAPI authentication is enabled, but the likelihood of
successful exploitation appears remote.
This could only affect RHEL4 as previous RHEL did not support GSSAPI
I've done some analysis of this issue and received a mail from Mark Dowd
regarding this vulnerability. The upstream details are misleading.
The problem is that the signal handling in openssh does quite a lot and can
introduce a race condition during cleanup. This flaw could possibly cause a
double free condition within the kerberos cleanup code. The GSSAPI code is
completely harmless, upstream calling this issue a GSSAPI issue leads me to
believe they did not analyze, nor try to understand this issue.
There is also PAM cleanup code which is executed. This PAM source hasn't been
investigated so the possible outcome is currently unknown.
Red Hat will be fixing this issue due to the incredible complexity and possible
danger. This is a case of better safe than sorry.
This issue also likely affects RHEL3
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.