Threats / Linux / CVE-2021-3493
CVE-2021-3493
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Linux Kernel vulnerability
The overlayfs stacking file system in the Linux kernel improperly validates file capabilities against user namespaces, enabling privilege escalation.
Verdict
Today item — known-exploited.
A local attacker can exploit improper capability validation in overlayfs to gain elevated privileges. The vulnerability affects user namespace isolation and has been actively exploited in the wild.
01
Is it exploitable?
— the evidence, ranked above the scoreExploit available
Public proof-of-concept exploit code is cataloged for this vulnerability.We link the existence of the exploit; we do not host or redistribute payloads.
Reported exploitation
1 independent public report of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-10-20).
Probability (EPSS)
EPSS 0.43988 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Linux, Kernel. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-862 Missing Authorization — weakness family: Authorization / access control.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious file with capabilities in an overlayfs mount to bypass namespace restrictions.
Business
Unauthorized privilege escalation exposes the system to complete compromise by local users.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I leverage the capability validation flaw to execute code with elevated privileges within a container or user namespace.
Business
Container isolation is broken, allowing escape and lateral movement to the host system.
3
Lateral reach — past segmentation narrative 3
Attacker
I gain root or system-level access through the privilege escalation path.
Business
Full system control enables data theft, malware installation, and persistent compromise.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05