Gentoo: rssh, scponly Unrestricted command execution
Posted by Joe Shakespeare   
Gentoo rssh and scponly do not filter command-line options that can be exploited to execute any command, thereby allowing a remote user to completely bypass the restricted shell.

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Gentoo Linux Security Advisory                           GLSA 200412-01
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                                            http://security.gentoo.org/
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  Severity: Normal
     Title: rssh, scponly: Unrestricted command execution
      Date: December 03, 2004
      Bugs: #72815, #72816
        ID: 200412-01

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Synopsis
========

rssh and scponly do not filter command-line options that can be
exploited to execute any command, thereby allowing a remote user to
completely bypass the restricted shell.

Background
==========

rssh and scponly are two restricted shells, allowing only a few
predefined commands. They are often used as a complement to OpenSSH to
provide access to remote users without providing any remote execution
privileges.

Affected packages
=================

    -------------------------------------------------------------------
     Package           /  Vulnerable  /                     Unaffected
    -------------------------------------------------------------------
  1  net-misc/scponly        < 4.0                              >= 4.0
  2  app-shells/rssh       <= 2.2.2                        Vulnerable!
    -------------------------------------------------------------------
     NOTE: Certain packages are still vulnerable. Users should migrate
           to another package if one is available or wait for the
           existing packages to be marked stable by their
           architecture maintainers.
    -------------------------------------------------------------------
     2 affected packages on all of their supported architectures.
    -------------------------------------------------------------------

Description
===========

Jason Wies discovered that when receiving an authorized command from an
authorized user, rssh and scponly do not filter command-line options
that can be used to execute any command on the target host.

Impact
======

Using a malicious command, it is possible for a remote authenticated
user to execute any command (or upload and execute any file) on the
target machine with user rights, effectively bypassing any restriction
of scponly or rssh.

Workaround
==========

There is no known workaround at this time.

Resolution
==========

All scponly users should upgrade to the latest version:

    # emerge --sync
    # emerge --ask --oneshot --verbose ">=net-misc/scponly-4.0"

Currently, there is no released version of rssh that contains a fix for
these issues. The author declared that he cannot provide a fixed
version at this time. Therefore, the rssh package has been hard-masked
prior to complete removal from Portage, and current users are advised
to unmerge the package.

References
==========

  [ 1 ] BugTraq Posting

http://www.securityfocus.com/archive/1/383046/2004-11-30/2004-12-06/0

Availability
============

This GLSA and any updates to it are available for viewing at
the Gentoo Security Website:

  http://security.gentoo.org/glsa/glsa-200412-01.xml

Concerns?
=========

Security is a primary focus of Gentoo Linux and ensuring the
confidentiality and security of our users machines is of utmost
importance to us. Any security concerns should be addressed to
security@gentoo.org or alternatively, you may file a bug at
http://bugs.gentoo.org.

License
=======

Copyright 2004 Gentoo Foundation, Inc; referenced text
belongs to its owner(s).

The contents of this document are licensed under the
Creative Commons - Attribution / Share Alike license.

http://creativecommons.org/licenses/by-sa/2.0