CVE-2021-3493
Linux Kernel Privilege Escalation Vulnerability
Linux Kernel
The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on files in an underlying file system. Due to the combination of unprivileged user namespaces along with a patch carried in the Ubuntu kernel to allow unprivileged overlay mounts, an attacker could use this to gain elevated privileges.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 20 October 2022. US federal agencies were required to remediate it by 10 November 2022.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 49.2%, which is higher than 98.9% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Frequently asked questions
Is CVE-2021-3493 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2021-3493.
What does CVE-2021-3493 affect?
CVE-2021-3493 affects Linux Kernel. The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on files in an underlying file system. Due to the combination of unprivileged user namespaces along with a patch carried in the Ubuntu kernel to allow unprivileged overlay mounts, an attacker could use this to gain elevated privileges.
How severe is CVE-2021-3493?
CVE-2021-3493 is rated HIGH with a CVSS base score of 8.8. EPSS puts the probability of exploitation in the next 30 days at 49.2%, higher than 98.9% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 10 November 2022.
How should organisations respond to CVE-2021-3493?
Apply the vendor patch for Linux Kernel as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.