CVE-2021-3493: Linux Kernel Privilege Escalation Vulnerability
Actively exploited. At least one CVE in this advisory is listed in the CISA Known Exploited Vulnerabilities catalog — exploitation has been observed in the wild. Treat remediation as urgent.
The overlayfs stacking file system in Linux kernel does not properly validate the application of file capabilities against user namespaces, which could lead to privilege escalation.
CSIRTS triage
- What
- The overlayfs stacking file system does not properly validate file capabilities, leading to privilege escalation.
- Who is affected
- Users of affected Linux kernel versions.
- Urgency
- Immediate action is required as the vulnerability is critical and actively exploited.
- Action
- Update to the latest Linux kernel version.
AI-assisted analysis generated from the source advisory — verify against the original.
⚡ Watch Kernel
Get an email when a new Kernel advisory drops — max one per day, one-click unsubscribe.
Details
Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-3493
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Exploitation confirmedCVE-2021-3493Already exploited in the wild (CISA KEV) — the prediction phase is over. Patch now. Riskier than 99% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2021-3493 | coverage & exploitation status | NVD · CVE.org |
Recent advisories for Linux Kernel Privilege
A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.
- medium[UPDATE] [medium] Linux Kernel: Vulnerability allows privilege escalationcert-bund · 2026-07-10
- high[UPDATE] [high] Linux Kernel: Vulnerability allows privilege escalationcert-bund · 2026-07-10
- high[UPDATE] [high] Linux Kernel: Vulnerability allows privilege escalationcert-bund · 2026-07-10
- medium[UPDATE] [medium] Linux Kernel: Vulnerability allows privilege escalation and denial of servicecert-bund · 2026-07-07
- high[UPDATE] [high] Linux Kernel: Multiple vulnerabilities allow denial of service and privilege escalationcert-bund · 2026-07-06
- unknownFragnesia Local Privilege Escalation report via ESP-in-TCP in the Linux Kernelaws · 2026-06-05
More from CISA Known Exploited Vulnerabilities
- criticalCVE-2026-48939: iCagenda Unrestricted Upload of File with Dangerous Type Vulnerability2026-07-10
- criticalCVE-2026-56291: Balbooa Forms Unrestricted Upload of File with Dangerous Type Vulnerability2026-07-10
- criticalCVE-2026-48908: JoomShaper SP Page Builder Unrestricted Upload of File with Dangerous Type Vulnerability2026-07-07
- criticalCVE-2026-55255: Langflow Authorization Bypass Through User-Controlled Key Vulnerability2026-07-07
- criticalCVE-2026-48282: Adobe ColdFusion Path Traversal Vulnerability2026-07-07