# CVE-2021-3492

## Summary

- **CVE ID:** CVE-2021-3492
- **Severity:** HIGH
- **CVSS Score:** 8.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H)
- **CWE:** CWE-415, CWE-401
- **Published:** Apr 17, 2021
- **Last Modified:** Mar 13, 2026

## Description

Shiftfs, an out-of-tree stacking file system included in Ubuntu Linux kernels, did not properly handle faults occurring during copy_from_user() correctly. These could lead to either a double-free situation or memory not being freed at all. An attacker could use this to cause a denial of service (kernel memory exhaustion) or gain privileges via executing arbitrary code. AKA ZDI-CAN-13562.

## Affected Products

- Ubuntu — Linux kernel (5.8 kernel)
- Ubuntu — Linux kernel (5.4 kernel)

## References

- [CNA](https://www.openwall.com/lists/oss-security/2021/04/16/2)
- [CNA](https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/?id=8fee52ab9da87d82bc6de9ebb3480fff9b4d53e6)
- [CNA](https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/?id=25c891a949bf918b59cbc6e4932015ba4c35c333)
- [CNA](https://ubuntu.com/security/notices/USN-4917-1)
- [CNA](https://www.zerodayinitiative.com/advisories/ZDI-21-422/)
- [CNA](http://packetstormsecurity.com/files/162614/Kernel-Live-Patch-Security-Notice-LSN-0077-1.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 24.44%
- **EPSS Percentile:** 96.0

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._