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Gentoo Linux Security Advisory                           GLSA 201603-04
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                                           https://security.gentoo.org/
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 Severity: Normal
    Title: FUSE: incorrect filtering of environment variables leading to
           privilege escalation
     Date: March 09, 2016
     Bugs: #550152
       ID: 201603-04

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Synopsis
=======
The fusermount binary in FUSE does not properly clear the environment
before invoking mount or umount as root that allows a local user to
overwrite arbitrary files.

Background
=========
FUSE provides an interface for filesystems implemented in userspace.

Affected packages
================
    -------------------------------------------------------------------
     Package              /     Vulnerable     /            Unaffected
    -------------------------------------------------------------------
  1  sys-fs/fuse                  < 2.9.4                    >= 2.9.4

Description
==========
The fusermount binary calls setuid(geteuid()) to reset the RUID when it
invokes /bin/mount so that it can use privileged mount options that are
normally restricted if RUID != EUID.  FUSE does not properly clear
environment variables before invoking mount or umount as root allowing
this to be passed to operations using elevated privileges such as
LIBMOUNT_MTAB that is used by the mount commands debugging feature.

Impact
=====
The FUSE vulnerability allows a local, unprivileged user to overwrite
arbitrary files on the system.

Workaround
=========
There is no known work around at this time.

Resolution
=========
All FUSE users should upgrade to the latest version:

  # emerge --sync
  # emerge --ask --oneshot --verbose ">=sys-fs/fuse-2.9.4"

References
=========
[ 1 ] CVE-2015-3202
      http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-3202

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

 https://security.gentoo.org/glsa/201603-04

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
https://bugs.gentoo.org.

License
======
Copyright 2016 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.

https://creativecommons.org/licenses/by-sa/2.5/