10-years-old Sudo bug lets Linux users gain root-level access

A major vulnerability impacting a large chunk of the Linux ecosystem has been patched today in Sudo, an app that allows admins to delegate limited root access to other users.

The vulnerability, which received a CVE identifier of CVE-2021-3156, but is more commonly known as “Baron Samedit,” was discovered by security auditing firm Qualys two weeks ago and was patched earlier today with the release of Sudo v1.9.5p2.

In a simple explanation provided by the Sudo team today, the Baron Samedit bug can be exploited by an attacker who has gained access to a low-privileged account to gain root access, even if the account isn’t listed in /etc/sudoers — a config file that controls which users are allowed access to su or sudo commands in the first place.

For the technical details behind this bug, please refer to the Qualys report or the video below.

While there have been two other Sudo security flaws disclosed over the past two years, the bug disclosed today is the one considered the most dangerous of all three.

The two previous bugs, CVE-2019-14287 (known as the -1 UID bug) and CVE-2019-18634 (known as the pwfeedback bug), were hard to exploit because they required complex and non-standard sudo setups.

Things are different for the bug disclosed today, which Qualys said impacts all Sudo installs where the sudoers file (/etc/sudoers) is present — which is usually found in most default Linux+Sudo installs.

Making matters worse, the bug also has a long tail. Qualys said the bug was introduced in the Sudo code back in July 2011, effectively impacting all Sudo versions released over the past ten years.

The Qualys team said they were able to independently verify the vulnerability and develop multiple exploit variants for Ubuntu 20.04 (Sudo 1.8.31), Debian 10 (Sudo 1.8.27), and Fedora 33 (Sudo 1.9.2).

“Other operating systems and distributions are also likely to be exploitable,” the security firm said.

All in all, the Baron Samedit vulnerabilities is one of the rare Sudo security flaws that can also be successfully weaponized in the real world, in comparison to the previous two bugs disclosed in years prior.

Qualys told ZDNet that if botnet operators brute-force low-level service accounts, the vulnerability could be abused in the second stage of an attack to help intruders easily gain root access and full control over a hacked server.

And as ZDNet reported on Monday, these types of botnets targeting Linux systems through brute-force attacks are quite common these days.

Today’s Sudo update should be applied as soon as possible to avoid unwanted surprises from both botnet operators or malicious insiders (rogue employees).