Serious 10-year-old flaw in Linux sudo command; a new version patches it

Linux users should immediately patch a serious vulnerability to the sudo command that, if exploited, can allow unprivileged users gain root privileges on the host machine.

Called Baron Samedit, the flaw has been “hiding in plain sight” for about 10 years, and was discovered earlier this month by researchers at Qualys and reported to sudo developers, who came up with patches Jan. 19, according to a Qualys blog. (The blog includes a video of the flaw being exploited.)

A new version of sudo—sudo v1.9.5p2—has been created to patch the problem, and notifications have been posted for many Linux distros including Debian, Fedora, Gentoo, Ubuntu, and SUSE, according to Qualys.

According to the common vulnerabilities and exposures (CVE) description of Baron Samedit (CVE-2021-3156), the flaw can be exploited “via ‘sudoedit -s’ and a command-line argument that ends with a single backslash character.”

According  to Qualys, the flaw was introduced in July 2011 and affects legacy versions from 1.8.2 to 1.8.31p2 as well as default configurations of versions from 1.9.0 to 1.9.5p1.

The purpose of sudo is for adminst to administer user system privileges.

For Ubuntu users, the patched sudo version appears to be related to the version of the OS you are running. The Ubuntu site shows this release-specific information for the flaw:

Ubuntu 21.04 (Hirsute Hippo) Released (1.9.4p2-2ubuntu2)
Ubuntu 20.10 (Groovy Gorilla) Released (1.9.1-1ubuntu1.1)
Ubuntu 20.04 LTS (Focal Fossa) Released (1.8.31-1ubuntu1.2)
Ubuntu 18.04 LTS (Bionic Beaver) Released (1.8.21p2-3ubuntu1.4)
Ubuntu 16.04 LTS (Xenial Xerus) Released (1.8.16-0ubuntu1.10)
Ubuntu 14.04 ESM (Trusty Tahr) Released (1.8.9p5-1ubuntu1.5+esm6)

Use the sudo -version command to view which release you are running. Checking sudo on a 20.04 system, for example, you might see this:

$ sudo —version
Sudo version 1.8.31
Sudoers policy plugin version 1.8.31
Sudoers file grammar version 46
Sudoers I/O plugin version 1.8.31

Another way to determine if your systems are vulnerable is to run a command such as sudoedit -s /. If the command returns a usage statement, your system is OK. If it returns an error starting with “sudoedit”, you need the patch.