oss-sec mailing list archives
Re: openssh on linux rce in sftp-only mode
From: Yves-Alexis Perez <corsac () debian org>
Date: Thu, 09 Oct 2014 09:49:38 +0200
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
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Current thread:
- openssh on linux rce in sftp-only mode Hanno Böck (Oct 08)
- Re: openssh on linux rce in sftp-only mode Jann Horn (Oct 08)
- Re: openssh on linux rce in sftp-only mode Josh Bressers (Oct 08)
- Re: openssh on linux rce in sftp-only mode Jann Horn (Oct 08)
- Re: openssh on linux rce in sftp-only mode Josh Bressers (Oct 08)
- Re: openssh on linux rce in sftp-only mode Jann Horn (Oct 08)
- Re: openssh on linux rce in sftp-only mode Yves-Alexis Perez (Oct 09)
- Re: openssh on linux rce in sftp-only mode Josh Bressers (Oct 08)
- Re: openssh on linux rce in sftp-only mode Vitor Ventura (Oct 09)
- Re: openssh on linux rce in sftp-only mode Jann Horn (Oct 08)