Public proof of conceptFix available

CVE-2021-3492

Q: Is CVE-2021-3492 actively exploited?

Active exploitation of CVE-2021-3492 has not been confirmed. Its EPSS score was 1.5% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-3492?

CVE-2021-3492 has a CVSS v3 base score of 7.8 (HIGH severity), with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

A public proof of concept exists; no exploitation attested.

Published2021-04-17
Fixed in20.10 · 20.04 · 18.04
WeaknessCWE-401 · CWE-415

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Shiftfs, an out-of-tree stacking file system included in Ubuntu Linux kernels, did not properly handle faults occurring during copy_from_user() correctly. These could lead to either a double-free situation or memory not being freed at all. An attacker could use this to cause a denial of service (kernel memory exhaustion) or gain privileges via executing arbitrary code. AKA ZDI-CAN-13562.

Timeline

dates in UTC

2021-04-1705:15CVE publishedNVD
2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-3492?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-3492?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Canonical ubuntu linux

Branch	Affected	Fixed in	Source
20.10	< 20.10	20.10	NVD
20.4	≥ 18.04.1, < 20.04	20.04	NVD
18.4	< 18.04	18.04	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Canonical ubuntu linux to 20.10 · 20.04 · 18.04

Advisories and patches

git.launchpad.netPatch · Vendor Advisory
git.launchpad.netPatch · Vendor Advisory
ubuntu.comVendor Advisory

Detection

read 2026-10-23 19:23 UTC

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: 1 repository, unverifiedsynacktiv/CVE-2021-3492

Sources

CNACVSS 3.18.8read 2026-10-23
NVDCVSS 3.17.8read 2026-10-23
NVDCVSS 2.07.2read 2026-10-23
CNAweakness (CWE)CWE-401, CWE-415read 2026-10-23
NVDweakness (CWE)CWE-401, CWE-415read 2026-10-23
FIRST EPSSEPSS score1.5 %2026-10-23
PoC-in-GitHubproof of concept1read 2026-10-23

Technical details

CVSS v3 Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Published: 2021-04-17
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-3492?

Is CVE-2021-3492 actively exploited?

Active exploitation of CVE-2021-3492 has not been confirmed. Its EPSS score was 1.5% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-3492?

CVE-2021-3492 has a CVSS v3 base score of 7.8 (HIGH severity), with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

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