CVE-2026-74937: Use-after-free in the JavaScript: GC component

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-18 · updated 2026-08-19
Weakness: CWE-416

Description

Use-after-free in the JavaScript: GC component. This vulnerability was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.

Affected products

Mozilla Firefox: before 153.1.0; before 154.0.0 — fixed in 153.1.0, 154.0.0
Mozilla Thunderbird: before 153.1.0; before 154.0 — fixed in 153.1.0, 154.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 153.1.0, 154.0.0; Mozilla Thunderbird 153.1.0, 154.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2053337
https://www.mozilla.org/security/advisories/mfsa2026-74/
https://www.mozilla.org/security/advisories/mfsa2026-77/
https://www.mozilla.org/security/advisories/mfsa2026-78/
https://www.mozilla.org/security/advisories/mfsa2026-80/

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