CVE-2021-3493

Ubuntu OverlayFS Local Privesc

Affected Versions

Ubuntu 20.10
Ubuntu 20.04 LTS
Ubuntu 18.04 LTS
Ubuntu 16.04 LTS
Ubuntu 14.04 ESM

Usage

gcc exploit.c -o exploit
chmod +x exploit
./exploit

Description

"Ubuntu specific issue in the overlayfs file system in the Linux kernel where it did not properly validate the application of file system capabilities with respect to user namespaces. A local attacker could use this to gain elevated privileges, due to a patch carried in Ubuntu to allow unprivileged overlayfs mounts." - Ubuntu Security

Fixed in Linux 5.11

References

https://ssd-disclosure.com/ssd-advisory-overlayfs-pe/
https://ubuntu.com/security/CVE-2021-3493
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52
https://www.openwall.com/lists/oss-security/2021/04/16/1

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