Date: Thu, 09 Oct 2014 09:49:38 +0200 From: Yves-Alexis Perez <corsac@...ian.org> To: oss-security@...ts.openwall.com Subject: Re: openssh on linux rce in sftp-only mode On jeu., 2014-10-09 at 01:05 +0200, Jann Horn wrote: > On Wed, Oct 08, 2014 at 06:44:32PM -0400, Josh Bressers wrote: > > > > > > > > I think one has to assume if a user has unrestricted sftp access, they can > > > > figure out how to do most anything. Even with the upstream hardening patch, > > > > it really only protects the sftpd process. Any other processes the user may > > > > own could be modified. > > > > > > Not that easily - /proc/$pid/mem requires you to either be the same process > > > or be attached to it via ptrace, I think. > > > > > > > I can't speak for other systems (I don't understand the details), but I can > > read arbitrary process memory for processes I own in Fedora 20. > > Hmm, just tried it on Debian Testing, I can reproduce that. > > > > Does someone know what the typical default is? > > I looked through the git history of fs/proc/base.c now, looks like commit > e268337dfe26dfc7efd422a804dbb27977a3cccc ("proc: clean up and fix > /proc/<pid>/mem handling") changed the behavior to be more permissive. That commit > is between kernel 3.2 and 3.3. Meh. :( Note that you can somehow restrict ptrace using Yama with kernel.yama.ptrace_scope (see https://www.kernel.org/doc/Documentation/security/Yama.txt) If would like to restrict sftp users on a somehow hardened box, it might make sense to set ptrace_scope to 1+. Regards, -- Yves-Alexis Download attachment "signature.asc" of type "application/pgp-signature" (474 bytes)
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