What’s Vulnerable › Vulnerabilities
CVE-2021-3492: Ubuntu linux kernel shiftfs file system double free vulnerability
- Severity: high (CVSS 7.8 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 1.5% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2021-04-17 · updated 2026-06-17
- Weakness: CWE-401
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
- Canonical Ubuntu Linux: before 18.04; from 18.04.1 before 20.04; before 20.10 — fixed in 18.04, 20.04, 20.10
How to fix
Upgrade to a fixed version: Canonical Ubuntu Linux 18.04, 20.04, 20.10. Check the vendor advisory for mitigations.
References
- http://packetstormsecurity.com/files/162614/Kernel-Live-Patch-Security-Notice-LSN-0077-1.html
- https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/?id=25c891a949bf918b59cbc6e4932015ba4c35c333
- https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/?id=8fee52ab9da87d82bc6de9ebb3480fff9b4d53e6
- https://ubuntu.com/security/notices/USN-4917-1
- https://www.openwall.com/lists/oss-security/2021/04/16/2
- https://www.zerodayinitiative.com/advisories/ZDI-21-422/
- http://packetstormsecurity.com/files/162614/Kernel-Live-Patch-Security-Notice-LSN-0077-1.html
- https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/?id=25c891a949bf918b59cbc6e4932015ba4c35c333
- https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/?id=8fee52ab9da87d82bc6de9ebb3480fff9b4d53e6
- https://ubuntu.com/security/notices/USN-4917-1
- https://www.openwall.com/lists/oss-security/2021/04/16/2
- https://www.zerodayinitiative.com/advisories/ZDI-21-422/
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