What’s Vulnerable › Vulnerabilities

CVE-2025-4918: Out-of-bounds access when resolving Promise objects

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 9.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2025-05-17 · updated 2026-09-30
• Weakness: CWE-125

Description

An attacker was able to perform an out-of-bounds read or write on a JavaScript `Promise` object. This vulnerability was fixed in Firefox 138.0.4, Firefox ESR 128.10.1, Firefox ESR 115.23.1, Thunderbird 128.10.2, and Thunderbird 138.0.2.

Affected products

• Mozilla Firefox: before 115.23.1; before 138.0.4; from 116.0 before 128.10.1 — fixed in 115.23.1, 128.10.1, 138.0.4
• Mozilla Thunderbird: before 128.10.2; from 138.0 before 138.0.2 — fixed in 128.10.2, 138.0.2

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.23.1, 128.10.1, 138.0.4; Mozilla Thunderbird 128.10.2, 138.0.2. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1966612
• https://www.mozilla.org/security/advisories/mfsa2025-36/
• https://www.mozilla.org/security/advisories/mfsa2025-37/
• https://www.mozilla.org/security/advisories/mfsa2025-38/
• https://www.mozilla.org/security/advisories/mfsa2025-40/
• https://www.mozilla.org/security/advisories/mfsa2025-41/
• https://lists.debian.org/debian-lts-announce/2025/05/msg00024.html
• https://lists.debian.org/debian-lts-announce/2025/05/msg00046.html
• https://www.vicarius.io/vsociety/posts/cve-2025-4918-detect-firefox-out-of-bounds-write
• https://www.vicarius.io/vsociety/posts/cve-2025-4918-mitigate-firefox-out-of-bounds-write

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