fuse 2.8.5 and earlier does not properly handle when /etc/mtab cannot be updated, which allows local users to unmount arbitrary directories via a symlink attack.

Race conditions in fuse allowed unprivileged users to umount arbitrary mount points (CVE-2011-0541,CVE-2010-3879,CVE-2011-0543).

From Red Hat Security Advisory 2011:1083 :

Updated fuse packages that fix multiple security issues are now available for Red Hat Enterprise Linux 6.

The Red Hat Security Response Team has rated this update as having moderate security impact. Common Vulnerability Scoring System (CVSS) base scores, which give detailed severity ratings, are available for each vulnerability from the CVE links in the References section.

FUSE (Filesystem in Userspace) can implement a fully functional file system in a user-space program. These packages provide the mount utility, fusermount, the tool used to mount FUSE file systems.

Multiple flaws were found in the way fusermount handled the mounting and unmounting of directories when symbolic links were present. A local user in the fuse group could use these flaws to unmount file systems, which they would otherwise not be able to unmount and that were not mounted using FUSE, via a symbolic link attack.
(CVE-2010-3879, CVE-2011-0541, CVE-2011-0542, CVE-2011-0543)

Note: The util-linux-ng RHBA-2011:0699 update must also be installed to fully correct the above flaws.

All users should upgrade to these updated packages, which contain backported patches to correct these issues.

The following security issues were fixed in fuse :

  - FUSE allowed local users to create mtab entries with     arbitrary pathnames, and consequently unmount any     filesystem, via a symlink attack on the parent directory     of the mountpoint of a FUSE filesystem. (CVE-2010-3879)

  - Avoid mounting a directory including evaluation of     symlinks, which might have allowed local attackers to     mount filesystems anywhere in the system.
    (CVE-2011-0541)

  - Avoid symlink attacks on the mount point written in the     mtab file. (CVE-2011-0543)

Updated fuse packages that fix multiple security issues are now available for Red Hat Enterprise Linux 6.

The Red Hat Security Response Team has rated this update as having moderate security impact. Common Vulnerability Scoring System (CVSS) base scores, which give detailed severity ratings, are available for each vulnerability from the CVE links in the References section.

FUSE (Filesystem in Userspace) can implement a fully functional file system in a user-space program. These packages provide the mount utility, fusermount, the tool used to mount FUSE file systems.

Multiple flaws were found in the way fusermount handled the mounting and unmounting of directories when symbolic links were present. A local user in the fuse group could use these flaws to unmount file systems, which they would otherwise not be able to unmount and that were not mounted using FUSE, via a symbolic link attack.
(CVE-2010-3879, CVE-2011-0541, CVE-2011-0542, CVE-2011-0543)

Note: The util-linux-ng RHBA-2011:0699 update must also be installed to fully correct the above flaws.

All users should upgrade to these updated packages, which contain backported patches to correct these issues.

The following security issues were fixed in fuse and util-linux :

  - FUSE allowed local users to create mtab entries with     arbitrary pathnames, and consequently unmount any     filesystem, via a symlink attack on the parent directory     of the mountpoint of a FUSE filesystem. (CVE-2010-3879)

  - Avoid mounting a directory including evaluation of     symlinks, which might have allowed local attackers to     mount filesystems anywhere in the system.
    (CVE-2011-0541)

  - Avoid symlink attacks on the mount point written in the     mtab file. (CVE-2011-0543)

Additional two bugs were fixed in util-linux :

  - fixed retrying nfs mounts on rpc timeouts

  - allow seperate control of the internet protocol uses by     rpc.mount seperately of the protocol used by nfs.

New features were implemented: - mount now has --fake and
--no-canonicalize options, required for the symlink security fixes.
These were backported from mainline.

The following security issues were fixed :

  - FUSE allowed local users to create mtab entries with     arbitrary pathnames, and consequently unmount any     filesystem, via a symlink attack on the parent directory     of the mountpoint of a FUSE filesystem. (CVE-2010-3879)

  - Avoid mounting a directory including evaluation of     symlinks, which might have allowed local attackers to     mount filesystems anywhere in the system.
    (CVE-2011-0541)

  - Avoid symlink attacks on the mount point written in the     mtab file. Four bugs were fixed:. (CVE-2011-0543)

  - fixed retrying nfs mounts on rpc timeouts

  - allow seperate control of the internet protocol uses by     rpc.mount seperately of the protocol used by nfs.

  - Fixed locking in libuuid/uuid to avoid duplicate uuids.

  - mkswap bad block check marked every block bad in O(n!)     time on a good device New features were implemented :

  - mount now has --fake and --no-canonicalize options,     required for the symlink security fixes. These were     backported from mainline.

  - mount can now auto-detect and differentiate between     squashfs3 and squashfs (v4) filesystems, allowing     backward compatibility to the SUSE Linux Enterprise 11     GA codebase.

It was discovered that FUSE would incorrectly follow symlinks when checking mountpoints under certain conditions. A local attacker, with access to use FUSE, could unmount arbitrary locations, leading to a denial of service.

Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

ID	Name	Product	Family	Severity
75508	openSUSE Security Update : fuse (openSUSE-SU-2011:0264-1)	Nessus	SuSE Local Security Checks	medium
68309	Oracle Linux 6 : fuse (ELSA-2011-1083)	Nessus	Oracle Linux Local Security Checks	medium
57257	SuSE 10 Security Update : fuse (ZYPP Patch Number 7418)	Nessus	SuSE Local Security Checks	medium
55635	RHEL 6 : fuse (RHSA-2011:1083)	Nessus	Red Hat Local Security Checks	medium
53724	openSUSE Security Update : fuse (openSUSE-SU-2011:0265-1)	Nessus	SuSE Local Security Checks	medium
53256	SuSE 10 Security Update : FUSE (ZYPP Patch Number 7362)	Nessus	SuSE Local Security Checks	medium
53231	SuSE 11.1 Security Update : FUSE (SAT Patch Number 4095)	Nessus	SuSE Local Security Checks	medium
52479	Ubuntu 8.04 LTS / 9.10 / 10.04 LTS / 10.10 : fuse vulnerabilities (USN-1077-1)	Nessus	Ubuntu Local Security Checks	low

Detections

Analytics

CVE-2011-0541

critical

Tenable Plugins

medium

medium

medium

medium

medium

medium

medium

low