[Bug 2019] After a possible buffer overflow attack sshd does not accept connections any longer.

[bugzilla-daemon at bugzilla.mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=2019

Darren Tucker <dtucker at zip.com.au> changed:

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                 CC|                            |dtucker at zip.com.au

--- Comment #1 from Darren Tucker <dtucker at zip.com.au> 2012-06-17 13:39:30 EST ---
There's not a lot of information to go on here.  My guess is that the
main sshd is running out of file descriptors but that's only a guess.

Can you reproduce the problem with the current version of OpenSSH? 
What exactly does this "Regina Scan" thing send to sshd?  Does it make
lots of separate connections in parallel or in series?  What version of
HPUX are you using and does it have a native /dev/random device?  If
not, are you using prngd?  What's the ulimit setting for number of
files (ulimit -n)?

A couple of possible workarounds:
1) increase the number of file descriptors in whichever script starts
sshd (ie put "ulimit -n 4096" or some suitably large number somewhere
before sshd is invoked).
2) Reduce MaxStartups to, say, half of what it's currently set to. 
This will mean that you'll have less unauthenticated connections at any
time which should reduce the peak number of descriptors in use.
3) run sshd with the (undocumented) "-r" flag, which will turn off the
reexec behaviour, which will also reduce the number of descriptors in
use.  Note that this will also disable the protection of any run-time
randomization (ASLR, stack cookies and such) so if your OS actually
provides any of these things you'll actually be *more* at risk.

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