Buffer overflow in Mozilla Firefox
CVE-2026-74987
Internally found bugs present in Thunderbird ESR 140.13, Thunderbird ESR 153.0 and Thunderbird 153. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.
Vulnerability class: Buffer Overflow
Published · last modified .
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: 0.007 (52.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 52nd percentile — 52.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.007 · change: +0.002
Affected products
Weakness classification (CWE)
References
- bugzilla.mozilla.org/buglist.cgi (Broken Link)
- bugzilla.mozilla.org/buglist.cgi (Broken Link)
- bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
- www.mozilla.org/security/advisories/mfsa2026-74/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-76/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-77/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-78/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-79/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-80/ (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-74987?
- CVE-2026-74987 is a critical-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 9.8/10. Published 2026-08-18.
- How severe is CVE-2026-74987?
- Critical severity. CVSS v3 base score is 9.8 out of 10.