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util-linux: umount command validation error


1.  Gentoo Linux Security Advisory

Version Information

Advisory Reference GLSA 200509-15 / util-linux
Release Date September 20, 2005
Latest Revision September 20, 2005: 01
Impact high
Exploitable local
Package Vulnerable versions Unaffected versions Architecture(s)
sys-apps/util-linux < 2.12q-r3 >= 2.12q-r3 All supported architectures

Related bugreports: #105805


A command validation error in umount can lead to an escalation of privileges.

2.  Impact Information


util-linux is a suite of useful Linux programs including umount, a program used to unmount filesystems.


When a regular user mounts a filesystem, they are subject to restrictions in the /etc/fstab configuration file. David Watson discovered that when unmounting a filesystem with the '-r' option, the read-only bit is set, while other bits, such as nosuid or nodev, are not set, even if they were previously.


An unprivileged user facing nosuid or nodev restrictions can umount -r a filesystem clearing those bits, allowing applications to be executed suid, or have device nodes interpreted. In the case where the user can freely modify the contents of the filesystem, privilege escalation may occur as a custom program may execute with suid permissions.

3.  Resolution Information


Two workarounds exist, first, the suid bit can be removed from the umount utility, or users can be restricted from mounting and unmounting filesystems in /etc/fstab.


All util-linux users should upgrade to the latest version:

Code Listing 3.1: Resolution

# emerge --sync
# emerge --ask --oneshot --verbose ">=sys-apps/util-linux-2.12q-r3"

4.  References


Page updated September 20, 2005

Summary: This is a Gentoo Linux Security Advisory

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