CVE-2025-0247: Memory safety bugs fixed in Firefox 134 and Thunderbird 134

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 10.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-01-07 · updated 2026-10-05
Weakness: CWE-787

Description

Memory safety bugs present in Firefox 133 and Thunderbird 133. 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 134 and Thunderbird 134.

Affected products

Mozilla Firefox: before 134.0 — fixed in 134.0
Mozilla Thunderbird: before 134.0 — fixed in 134.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 134.0; Mozilla Thunderbird 134.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=1835193%2C1910021%2C1919803%2C1931576%2C1931948%2C1932173
https://www.mozilla.org/security/advisories/mfsa2025-01/
https://www.mozilla.org/security/advisories/mfsa2025-04/

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