What’s Vulnerable › Vulnerabilities

CVE-2025-0243: Memory safety bugs fixed in Firefox 134, Thunderbird 134, Firefox ESR 128.6, and Thunderbird 128.6

• Severity: medium (CVSS 5.1 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: 2025-01-07 · updated 2026-10-05
• Weakness: CWE-787

Description

Memory safety bugs present in Firefox 133, Thunderbird 133, Firefox ESR 128.5, and Thunderbird 128.5. 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, Firefox ESR 128.6, Thunderbird 134, and Thunderbird 128.6.

Affected products

• Mozilla Firefox: before 128.6.0; before 133.0 — fixed in 128.6.0, 133.0
• Mozilla Thunderbird: before 128.6.0; from 129.0 before 134.0 — fixed in 128.6.0, 134.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 128.6.0, 133.0; Mozilla Thunderbird 128.6.0, 134.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/buglist.cgi?bug_id=1827142%2C1932783
• https://www.mozilla.org/security/advisories/mfsa2025-01/
• https://www.mozilla.org/security/advisories/mfsa2025-02/
• https://www.mozilla.org/security/advisories/mfsa2025-04/
• https://www.mozilla.org/security/advisories/mfsa2025-05/
• https://lists.debian.org/debian-lts-announce/2025/01/msg00004.html

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