## https://sploitus.com/exploit?id=3394A0E9-2040-542F-8388-BF345AB29624
# CVE-2021-3493 โ Ubuntu OverlayFS Local Privilege Escalation
**Ubuntu-specific vulnerability in OverlayFS allowing unprivileged users to gain root privileges.**
> "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."
> โ Ubuntu Security
## Overview
This is a proof-of-concept exploit for **CVE-2021-3493**, a local privilege escalation vulnerability affecting several Ubuntu versions due to incorrect handling of file capabilities in user namespaces when using OverlayFS.
The exploit sets full capabilities (`cap_sys_admin+ep`, etc.) on a binary inside an OverlayFS mount inside a user namespace โ a combination that Ubuntu's backport accidentally made dangerous.
**Fixed upstream** in Linux kernel **5.11**.
## Affected Distributions / Versions
- Ubuntu 20.10
- Ubuntu 20.04 LTS
- Ubuntu 19.04
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS
- Ubuntu 14.04 ESM
**Not affected**:
- Official upstream kernels before Ubuntu's unprivileged mount patch
- Ubuntu versions with the security update applied (see Ubuntu's tracker)
โ Official Ubuntu security page: https://ubuntu.com/security/CVE-2021-3493
## Exploit
### Requirements
- Vulnerable Ubuntu version (unpatched)
- gcc (for compilation)
### Build & Run
```bash
# Compile as static binary (recommended)
gcc -static kernel_exploit.c -o exploit
# Make executable
chmod +x exploit
# Run the exploit
./exploit