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Date: Wed, 8 Oct 2014 11:07:59 +0200
From: Hanno Böck <>
To: OSS Security List <>
Subject: openssh on linux rce in sftp-only mode

This seems CVE-worthy:

"OpenSSH lets you grant SFTP access to users without allowing full
command execution using "ForceCommand internal-sftp". However, if you
misconfigure the server and don't use ChrootDirectory, the user will be
able to access all parts of the filesystem that he has access to -
including procfs. On modern Linux kernels (>=2.6.39, I
think), /proc/self/maps reveals the memory layout and /proc/self/mem
lets you write to arbitrary memory positions. Combine those and you get
easy RCE."

It involves a number of issues coming together, however in the end it
is an RCE with a legit configuration.

 * sftp-server(8): On platforms that support it, use prctl() to
   prevent sftp-server from accessing /proc/self/{mem,maps}

Hanno Böck


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