What is CVE-2021-29962?

CVE-2021-29962 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Resource Shutdown or Release. CVSS score: 4.3/10. Published 2021-06-24.

How severe is CVE-2021-29962?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Vulnerability in Mozilla Firefox

CVE-2021-29962

Firefox for Android would become unstable and hard-to-recover when a website opened too many popups. *This bug only affects Firefox for Android. Other operating systems are unaffected.*. This vulnerability affects Firefox < 89.

Published 2021-06-24 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L.

EPSS exploit prediction

EPSS: 0.007 (53.2th percentile), scored 2026-10-04.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 53rd percentile — 53.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: 0.000

Affected products

Mozilla Firefox — versions unspecified

Weakness classification (CWE)

CWE-404 — Improper Resource Shutdown or Release

References

www.mozilla.org/security/advisories/mfsa2021-23/ (Release Notes, Vendor Advisory)
bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Vendor Advisory)

Frequently asked questions

What is CVE-2021-29962?: CVE-2021-29962 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Resource Shutdown or Release. CVSS score: 4.3/10. Published 2021-06-24.
How severe is CVE-2021-29962?: Medium severity. CVSS v3 base score is 4.3 out of 10.