What is CVE-2026-5735?

CVE-2026-5735 is a critical-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-04-07.

How severe is CVE-2026-5735?

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

Buffer overflow in Mozilla Firefox

CVE-2026-5735

Memory safety bugs present in Firefox 149.0.1 and Thunderbird 149.0.1. 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 vulne…

Vulnerability class: Buffer Overflow

EPSS: 0.001 (18.0th percentile) — read the EPSS interpretation.

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.

Affected products

Mozilla Firefox — versions 149.0.2
Mozilla Thunderbird — versions 149.0.2

Weakness classification (CWE)

References

Memory safety bugs fixed in Firefox 149.0.2 and Thunderbird 149.0.2 (Issue Tracking, Broken Link)
security@mozilla.org (Vendor Advisory)
security@mozilla.org

Frequently asked questions

What is CVE-2026-5735?: CVE-2026-5735 is a critical-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-04-07.
How severe is CVE-2026-5735?: Critical severity. CVSS v3 base score is 9.8 out of 10.