CVE-2025-3034: Memory safety bugs fixed in Firefox 137 and Thunderbird 137

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-04-01 · updated 2026-09-30
Weakness: CWE-787

Description

Memory safety bugs present in Firefox 136 and Thunderbird 136. 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 137 and Thunderbird 137.

Affected products

Mozilla Firefox: before 137.0 — fixed in 137.0
Mozilla Thunderbird: before 137.0 — fixed in 137.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 137.0; Mozilla Thunderbird 137.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=1894100%2C1934086%2C1950360
https://www.mozilla.org/security/advisories/mfsa2025-20/
https://www.mozilla.org/security/advisories/mfsa2025-23/

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