Hello everyone,
A couple of days back, a serious heap-based buffer overflow has been discovered in sudo that is exploitable by any local user. It has been given the name Baron Samedit by its discoverer. The bug can be leveraged to elevate privileges to root, even if the user is not listed in the sudoers file. User authentication is not required to exploit the bug. It is commonly referred as CVE-2021-3156.
See it in action
You can see it in action here that several security researchers have recorded.
Sudo versions affected:
Sudo versions 1.8.2 through 1.8.31p2 and 1.9.0 through 1.9.5p1 are affected.
Keep in mind: Unless the patches have been backported, as is the case for Ubuntu 18.04, in which case it may not need to be 1.9.5p2
Are you vulnerable?
USE WITH CAUTION : Open your terminal and use sudo sudo -V to check your version number. See notes above for what versions are affected and read the note.
A More reliable way to check
Run sudoedit -s / to detect if you are vulnerable.
You can also try:
sudoedit -s '\' `perl -e 'print "A" x 65536'`
bonyt from hackernews pointed out that macOS doesn't have sudoedit, but you can make a symlink to it, as sudo is effectively a multi-call binary:
ln -s `which sudo` sudoedit
and then call it:
./sudoedit
Based on the response, It’s possible to understand if the host is vulnerable or not:
Vulnerable if responds an error starting with sudoedit: sudoedit: /: not a regular file or segfault
Not Vulnerable or patched if responds an error starting with usage:
Got containers or K8s?
Falco is the CNCF open-source project for runtime threat detection for containers and Kubernetes.
You can use a rule to detect and prevent if a user attempts it.
pawan328 from hackernews pointed out that you can view this blog post for additional details.
Fix it - the bug has been fixed in sudo 1.9.5p2
For Linux distros (that might be running on a Pi or a another computer) including WSL
sudo apt-get update
sudo apt-get --only-upgrade install sudo
Watch the Video
I have a video discussing this and showing all the methods shown above.
Which covers:
00:00 - Introduction
01:29 - What's a CVE?
02:22 - What's the bug?
05:30 - Exploit shown in action
13:07 - Sudo versions affected
13:48 - WSL Windows Subsystem for Linux
15:11 - Detecting if you are vulnerable through sudo (WSL)
19:21 - Detecting if you are vulnerable through sudo (Ubuntu)
20:53 - Detecting if you are vulnerable through commands
24:58 - What to do if you are running K8s or containers
27:54 - Examine Sudo versions
28:30 - Patching WSL
30:17 - Patching Ubuntu
32:09 - Where can I get exploit.c?
33:59 - Patching Ubuntu (part 2)
38:10 - Patching WSL (part 2)
46:35 - GitHub search results
47:28 - Patching WSL (part 3)
Conclusion
I stream on Twitch on Wednesday's at Noon PST and on Sat/Sun at 10 AM PST or you can watch the condensed version by subscribing to my YouTube.
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