CVE-2025-5272: Memory safety bugs fixed in Firefox 139 and Thunderbird 139

Severity: high (CVSS 7.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-05-27 · updated 2026-09-30
Weakness: CWE-787

Description

Memory safety bugs present in Firefox 138 and Thunderbird 138. 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 139 and Thunderbird 139.

Affected products

Mozilla Firefox: before 139.0 — fixed in 139.0
Mozilla Thunderbird: before 139.0 — fixed in 139.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 139.0; Mozilla Thunderbird 139.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=1726254%2C1742738%2C1960121
https://www.mozilla.org/security/advisories/mfsa2025-42/
https://www.mozilla.org/security/advisories/mfsa2025-45/

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