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.

CVSS 3.1

8.1CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

4.3% chance of exploitation in the next 30 days; higher than 90% of CVEs (scores of 2026-10-25)

CWE

CWE-119

Published

2025-06-24

Modified

2026-09-30

Record from

the NVD, synced 2026-10-19

Affected

• mozilla:firefox
• mozilla:thunderbird

References

• https://bugzilla.mozilla.org/buglist.cgi?bug_id=1941377%2C1960948%2C1966187%2C1966505%2C1970764%2C1942930
• https://www.mozilla.org/security/advisories/mfsa2025-51/
• https://www.mozilla.org/security/advisories/mfsa2025-54/

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