CVE-2021-3492: Ubuntu linux kernel shiftfs file system double free vulnerability
Last updated 27 August 2026
Other sources
Shiftfs, an out-of-tree stacking file system included in Ubuntu Linux kernels, did not properly handle faults occurring during copyfromuser() 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.
— Launchpad
This vulnerability allows local attackers to escalate privileges on affected installations of Canonical Ubuntu. An attacker must first obtain the ability to execute high-privileged code on the target system in order to exploit this vulnerability. The specific flaw exists within the ShiftFS module. The issue results from the lack of validating the existence of an object prior to performing further free operations on the object. An attacker can leverage this vulnerability to escalate privileges and execute code in the context of the kernel.
— ZDI
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
debian/linuxto a version that resolves this vulnerability.Fixed in 6.1.176-1Fixed in 6.1.187-1Fixed in 6.12.94-1Fixed in 6.12.107-1Fixed in 7.1.12-1Fixed in 7.1.13-1
Event History
Frequently Asked Questions
What is the severity of CVE-2021-3492?
CVE-2021-3492 has a medium severity level due to potential memory issues leading to vulnerabilities.
How do I fix CVE-2021-3492?
You can fix CVE-2021-3492 by upgrading to the recommended kernel versions such as 5.10.223-1, 5.10.226-1, 6.1.119-1, 6.1.123-1, 6.12.11-1, or 6.12.12-1.
Which versions of Ubuntu are affected by CVE-2021-3492?
CVE-2021-3492 affects Ubuntu versions from 18.04 up to 20.10.
What type of vulnerabilities does CVE-2021-3492 introduce?
CVE-2021-3492 may introduce double-free situations or situations where memory is not freed, increasing the risk of an attack.
Is CVE-2021-3492 an issue with just Ubuntu?
CVE-2021-3492 specifically affects the Shiftfs stacking file system in Ubuntu Linux kernels.