CVE-2026-6751: Uninitialized memory in the Audio/Video: Web Codecs component

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: 2026-04-21 · updated 2026-10-26
Weakness: CWE-457

Description

Uninitialized memory in the Audio/Video: Web Codecs component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

Affected products

Mozilla Firefox: before 140.10.0; before 150.0 — fixed in 140.10.0, 150.0
Mozilla Thunderbird: from 140.0 before 140.10.0 — fixed in 140.10.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 140.10.0, 150.0; Mozilla Thunderbird 140.10.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2025883
https://www.mozilla.org/security/advisories/mfsa2026-30/
https://www.mozilla.org/security/advisories/mfsa2026-32/
https://www.mozilla.org/security/advisories/mfsa2026-33/
https://www.mozilla.org/security/advisories/mfsa2026-34/
https://access.redhat.com/errata/RHSA-2026:10757
https://access.redhat.com/errata/RHSA-2026:10766
https://access.redhat.com/errata/RHSA-2026:10767
https://access.redhat.com/errata/RHSA-2026:12285
https://access.redhat.com/errata/RHSA-2026:13537
https://access.redhat.com/errata/RHSA-2026:15892
https://access.redhat.com/errata/RHSA-2026:17477

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