--- title: "CVE-2021-3493: Privilege Context Switching Error | CubePath" description: "The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on files…" language: en source: https://cubepath.com/security/cve/CVE-2021-3493 --- # CVE-2021-3493: Privilege Context Switching Error | CubePath ## Description 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. Official description from the CVE record, published by canonical. Copyright © 1999-2026 The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CVE license. [View the record on cve.org](https://www.cve.org/CVERecord?id=CVE-2021-3493) ## Key data ### CVSS 3.1 High 8.8 Score published by canonical in the CVE record. CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H | Metric | Value | What it means | | ---------------------- | ------- | ----------------------------------------------------------------------------------------- | | Attack vector | Local | The attacker needs local access to the system, or to trick a user into running something. | | Attack complexity | Low | No special conditions are needed. The attack can be repeated at will. | | Privileges required | Low | A basic user account is needed. | | User interaction | None | No action from any user is needed. | | Scope | Changed | The impact can reach other components beyond the vulnerable one. | | Confidentiality impact | High | Serious or total effect on the secrecy of data. | | Integrity impact | High | Serious or total effect on the trustworthiness of data. | | Availability impact | High | Serious or total effect on availability. | CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at [first.org/cvss](https://www.first.org/cvss/) . ### EPSS Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days. Score 0.49166 (49.2% probability) Percentile 98.9% Scores of Nov 10, 2026 Model v2026.06.15 ### CISA Known Exploited Vulnerabilities This CVE is listed in the CISA KEV catalog. Name in the catalog Linux Kernel Privilege Escalation Vulnerability Added to the catalog Oct 20, 2022 Federal due date Nov 10, 2022 ### CISA assessment as of Feb 7, 2025 Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA. Exploitation Recorded by CISA as active Automatable no Technical impact total ### Weakness (CWE) CWE catalog version 5.0. CWE names: Copyright © 2006-2026, The MITRE Corporation. See [/security/cve/legal](https://cubepath.com/security/cve/legal) for the CWE license. - [CWE-270](https://cwe.mitre.org/data/definitions/270.html) Privilege Context Switching Error ## Affected products Products listed in the CVE record, as the CNA published them. - Ubuntu linux kernel - affected: 5.8 kernel up to before 5.8.0-50.56 - affected: 5.4 kernel up to before 5.4.0-72.80 - affected: 4.15 kernel up to before 4.15.0-142.146 - affected: 4.4 kernel up to before 4.4.0-209.241 ## References Links listed in the CVE record. They lead to other sites, which CubePath does not control. - [ubuntu.com/security/notices/USN-4917-1](https://ubuntu.com/security/notices/USN-4917-1) - [git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/…](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52) - [openwall.com/lists/oss-security/2021/04/16/1](https://www.openwall.com/lists/oss-security/2021/04/16/1) - [packetstormsecurity.com/files/162434/Kernel-Live-Patch-Secu…](http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.html) - [packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local…](http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.html) - [packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local…](http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.html) ## Timeline 1. ID reserved Apr 12, 2021 2. Record published Apr 17, 2021 3. Added to CISA KEV Oct 20, 2022 4. Record last updated Oct 21, 2025 ## Look up another CVE ## About CubePath CubePath is a cloud provider with data centers in Europe and the United States. It offers VPS, bare metal servers and DDoS protection. [Cloud VPS](https://cubepath.com/vps) [DDoS protection](https://cubepath.com/ddos-protection) Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 20:03 UTC. [Sources and licenses](https://cubepath.com/security/cve/legal)