[Article] Security flaw in Sudo - Heap-Based Buffer Overflow allow root access

A new security flaw has been identified in the sudo software. Sudo, which is installed by default in many operating systems, is by default setuid root. This means that any shortcomings can lead to local users being able to obtain root permissions.

Over the years, sudo has also become larger and more features have been added. This has i.a. led to OpenBSD now having an option called doas.

Yesterday, the American security company Qualys reported that they had identified a vulnerability in sudo (CVE-2021-3156). The vulnerability allows a local user to exploit a heap vulnerability and thus become rooted. The bug has been around since 2011 and is found in the standard configuration. It is important to point out that it is included in the standard configuration, as many vulnerabilities discovered in sudo require special configurations.

The vulnerability is found in the set_cmnd () function and can be most easily triggered by using sudoedit and the following command:

sudoedit -s '\' `perl -e 'print "A" x 65536'` 

And if you are vulnerable, you get a segfault. Please note that you need a local account but not a member of sudoers or similar. And that not all installations have sudoedit, such as macOS.

Video from Qualys showing vulnerability:

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