Gentoo: FUSE mtab corruption through fusermount
Posted by Benjamin D. Thomas   
Gentoo The fusermount utility from FUSE can be abused to corrupt the /etc/mtab file contents, potentially allowing a local attacker to set unauthorized mount options.
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Gentoo Linux Security Advisory                           GLSA 200511-17
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                                            http://security.gentoo.org/
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  Severity: Normal
     Title: FUSE: mtab corruption through fusermount
      Date: November 22, 2005
      Bugs: #112902
        ID: 200511-17

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Synopsis
========

The fusermount utility from FUSE can be abused to corrupt the /etc/mtab
file contents, potentially allowing a local attacker to set
unauthorized mount options.

Background
==========

FUSE (Filesystem in Userspace) allows implementation of a fully
functional filesystem in a userspace program. The fusermount utility is
used to mount/unmount FUSE file systems.

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

    -------------------------------------------------------------------
     Package      /  Vulnerable  /                          Unaffected
    -------------------------------------------------------------------
  1  sys-fs/fuse     < 2.4.1-r1                            >= 2.4.1-r1

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

Thomas Biege discovered that fusermount fails to securely handle
special characters specified in mount points.

Impact
======

A local attacker could corrupt the contents of the /etc/mtab file by
mounting over a maliciously-named directory using fusermount,
potentially allowing the attacker to set unauthorized mount options.
This is possible only if fusermount is installed setuid root, which is
the default in Gentoo.

Workaround
==========

There is no known workaround at this time.

Resolution
==========

All FUSE users should upgrade to the latest version:

    # emerge --sync
    # emerge --ask --oneshot --verbose ">=sys-fs/fuse-2.4.1-r1"

References
==========

  [ 1 ] CVE-2005-3531
        http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2005-3531

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

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

  http://security.gentoo.org/glsa/glsa-200511-17.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 2005 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