CVE-2021-3493General(canonical / ubuntu_linux)

LOWCVSS 7.8 · HIGHCISA KEV

Exploit discussion active in current signal (1 latest mentions)

Immediate actions

Hunt for exploitation attempts and persistence artifacts
Increase monitoring for publicly documented tradecraft
Track advisory updates for patch or workaround availability

Recommended action window: High priority (within 72h)

NVD 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.

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1.5/ 10 priority

Sources & remediation

Listed in the CISA Known Exploited Vulnerabilities catalog. Federal remediation due date: 2022-11-10. Apply updates per vendor instructions.

Patch / fix

Exploit / PoC references

Vendor / third-party advisories

Other references

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3493

Weakness type (CWE)

CWE-270CWE-863

Priority

LOW

Exploitation

ACTIVE

PoC

YES

Patch

AVAILABLE

Momentum

STABLE

Are you affected?

If you run products in this scope, you should treat this CVE as relevant to your environment.

ubuntu_linux

Threat summary

Public PoC is present in monitored signal
3 mentions across 3 observed days
Momentum state: stable

What's happening

PoC mentioned or linked in 1 signal
Technical details provided in 3 signals
General: 2 classified signals
Peaked 2d ago at 1 mentions (2026-02-16); latest day: 1
3 total mentions across 3 days

Affected systems

Vendors

canonical

Products

ubuntu_linux

Deep dive

Activity timeline3 mentions / 3d

Signal classification2 categories

General

266.7%

PoC

133.3%

Referenced assets3 URLs

By indicator

Classification over time

Date	Total	Labels

2026-02-16	1	PoC1
2026-03-18	1	General1
2026-04-04	1	General1

Full discourse3 posts

Sun4lower@LittleSun4lower187d
General
I just completed OverlayFS - CVE-2021-3493 room on TryHackMe! Exploit a 2021 Kernel vulnerability in Ubuntu to become root almost instantly! https://tryhackme.com/room/overlayfs?utm_campaign=social_share&utm_medium=social&utm_content=room&utm_source=twitter&sharerId=66457951599dd28bfb000ded #tryhackme via @tryhackme #tryhackme #Consistency #learning
Post summary
The user completed a TryHackMe lab that demonstrates exploiting CVE‑2021-3493 for privilege escalation on Ubuntu, but no explicit PoC, exploit code, or active exploitation is discussed.
0000041
5 followersView on X
刘灏 LiuHao@GuanShanZhe204d
General
I just completed OverlayFS - CVE-2021-3493 room on TryHackMe! Exploit a 2021 Kernel vulnerability in Ubuntu to become root almost instantly! https://tryhackme.com/room/overlayfs?utm_campaign=social_share&utm_medium=social&utm_content=room&utm_source=twitter&sharerId=67c32163fcb8c49ab2766b1c #tryhackme 来自 @tryhackme
Post summary
The tweet references a TryHackMe room focused on CVE‑2021‑3493, noting that the exploitation was demonstrated, but provides no PoC, exploit code, patch advice, or evidence of wild attacks.
00000114
148 followersView on X
Ezekiel@Ezekieluche_234d
PoC
I just completed OverlayFS - CVE-2021-3493 room on TryHackMe! Exploit a 2021 Kernel vulnerability in Ubuntu to become root almost instantly! https://tryhackme.com/room/overlayfs?utm_campaign=social_share&utm_medium=social&utm_content=room&utm_source=twitter&sharerId=67ebda711f4b04b35fd07e05 #tryhackme via @tryhackme
Post summary
The tweet announces the completion of a TryHackMe room that walks through exploiting CVE‑2021‑3493 to gain root on Ubuntu systems. It references a training page but does not provide actual exploit code or mention real‑world attacks.
0000043
13 followersView on X

CPE platform detail2 entries

Part:

Vendor:

Product:

Version:

Target SW:

Target HW:

2 of 2 entries

Part	Vendor	Product	Version	Target SW	Target HW
OS	canonical	ubuntu_linux	-	-	-
OS	canonical	ubuntu_linux	-	-	-

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