What is CVE-2021-4120?

CVE-2021-4120 is a high-severity vulnerability in Canonical Ltd. Snapd, classified under Improper Input Validation. CVSS score: 8.2/10. Published 2022-02-17.

How severe is CVE-2021-4120?

High severity. CVSS v3 base score is 8.2 out of 10.

Is CVE-2021-4120 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Improper input validation in Canonical Ltd. Snapd

CVE-2021-4120

snapd 2.54.2 fails to perform sufficient validation of snap content interface and layout paths, resulting in the ability for snaps to inject arbitrary AppArmor policy rules via malformed content interface and layout declarations and hence escape strict snap confinement. Fixed in snapd versions 2.54.3+18.04, 2.54.3+20.04 and 2.54.3+21.10.1

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published 2022-02-17 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.2 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (36.5th percentile), scored 2026-10-19.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 37th percentile — 36.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

Canonical Ltd. Snapd — versions unspecified
Canonical Snapd
Canonical Ubuntu Linux — versions 18.04, 20.04, 21.10
Fedoraproject Fedora — versions 34, 35

Weakness classification (CWE)

CWE-20 — Improper Input Validation

Public proof-of-concept exploits

ARPSyndicate/cvemon

References

ubuntu.com/security/notices/USN-5292-1 (Patch, Vendor Advisory)
bugs.launchpad.net/snapd/+bug/1949368 (Exploit, Third Party Advisory, Issue Tracking)
www.openwall.com/lists/oss-security/2022/02/18/2 (mailing-list, Exploit, Mailing List, Third Party Advisory)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)

Frequently asked questions

What is CVE-2021-4120?: CVE-2021-4120 is a high-severity vulnerability in Canonical Ltd. Snapd, classified under Improper Input Validation. CVSS score: 8.2/10. Published 2022-02-17.
How severe is CVE-2021-4120?: High severity. CVSS v3 base score is 8.2 out of 10.
Is CVE-2021-4120 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.