Buffer overflow in Mozilla Firefox
CVE-2025-6436
Memory safety bugs present in Firefox 139 and Thunderbird 139. 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 was fixed in Firefox 140 and Thunderbird 140.
Vulnerability class: Buffer Overflow
EPSS: 0.029 (85.6th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
Affected products
- Mozilla Firefox — versions 140
- Mozilla Thunderbird — versions 140
Weakness classification (CWE)
References
- security@mozilla.org (Permissions Required)
- security@mozilla.org (Vendor Advisory)
- security@mozilla.org (Vendor Advisory)
Frequently asked questions
- What is CVE-2025-6436?
- CVE-2025-6436 is a high-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 8.1/10. Published 2025-06-24.
- How severe is CVE-2025-6436?
- High severity. CVSS v3 base score is 8.1 out of 10.