What is CVE-2020-6826?

CVE-2020-6826 is a critical-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2020-04-24.

How severe is CVE-2020-6826?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Mozilla Firefox

CVE-2020-6826

Mozilla developers Tyson Smith, Bob Clary, and Alexandru Michis reported memory safety bugs present in Firefox 74. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 75.

Vulnerability class: Buffer Overflow

Published 2020-04-24 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.014 (72.0th percentile), scored 2026-10-03.

Low probability of exploitation in the next 30 days, but still tracked. 72nd percentile — 72.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.012 · newest: 0.014 · change: +0.002

Affected products

Mozilla Firefox — versions unspecified

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

www.mozilla.org/security/advisories/mfsa2020-12/ (Vendor Advisory)
bugzilla.mozilla.org/buglist.cgi (Permissions Required, Issue Tracking)

Frequently asked questions

What is CVE-2020-6826?: CVE-2020-6826 is a critical-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2020-04-24.
How severe is CVE-2020-6826?: Critical severity. CVSS v3 base score is 9.8 out of 10.