FUSE: mtab corruption through fusermount

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.

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"