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Date: Fri, 21 Jul 2023 09:42:09 +0200
From: Marcus Meissner <meissner@...e.de>
To: oss-security@...ts.openwall.com
Subject: Re: Announce: OpenSSH 9.3p2 released
On Fri, Jul 21, 2023 at 11:04:49AM +1000, Matthew Fernandez wrote:
>
>
> On 7/20/23 23:41, Sevan Janiyan wrote:
> > On 20/07/2023 14:24, Demi Marie Obenour wrote:
> > > Should there be a system-wide configuration file containing a list
> > > of known-good PKCS#11 libraries? ssh-agent having to guess if
> > > something is a PKCS#11 library is less than awesome.
> >
> > There's a compile time setting for paths from which you are able to load
> > libraries from.
>
> I don’t think this helps much though, right? The Qualys research that
> motivated this found an exploit chain using only libs present in /usr/lib in
> a default Ubuntu install. If you want to lock down loading to a specific
> non-/usr/lib path that you have control over, this suggests you know and are
> in control of the PKCS#11 providers you’re going to support. In which case,
> why not avoid dynamic loading to begin with? I guess the allowlist and new
> defaults are the answer to this conundrum though.
The openssh fixing patches (besides disallowing this remote agent
behaviour by default) now just abort() the pkcs11 helper if they load a library
without the pkcs11 interface C_GetFunctionList() which should largely
solve the problem, unless a library can be exploited on first load.
Longrange thinking is if these kind of load/unload impacts could be
detected by tooling easily and/or get fixed in affected libraries.
Ciao, Marcus
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