What is CVE-2026-2779?

CVE-2026-2779 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 2026-02-24.

How severe is CVE-2026-2779?

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

Buffer overflow in Mozilla Firefox

CVE-2026-2779

Incorrect boundary conditions in the Networking: JAR component. This vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Vulnerability class: Buffer Overflow

Published 2026-02-24 · 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: 0.006 (45.7th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 46th percentile — 45.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: -0.000

Affected products

Mozilla Firefox — versions 140.8, 148
Mozilla Thunderbird — versions 140.8, 148

Weakness classification (CWE)

CWE-119 — Improper Restriction of Operations within the Bounds of a Memory Buffer

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking)
www.mozilla.org/security/advisories/mfsa2026-13/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-15/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-16/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-17/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-2779?: CVE-2026-2779 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 2026-02-24.
How severe is CVE-2026-2779?: Critical severity. CVSS v3 base score is 9.8 out of 10.