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Gentoo Linux Security Advisory 201603-04

Gentoo Linux Security Advisory 201603-04
Posted Mar 10, 2016
Authored by Gentoo | Site security.gentoo.org

Gentoo Linux Security Advisory 201603-4 - 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. Versions less than 2.9.4 are affected.

tags | advisory, arbitrary, local, root
systems | linux, gentoo
MD5 | a06b76d59d0e7ecf9f4dc5b13e759641

Gentoo Linux Security Advisory 201603-04

Change Mirror Download
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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.

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

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