CVE-2026-74981: Site isolation issue in the Audio/Video: Web Codecs component

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-18 · updated 2026-08-25
Weakness: CWE-346

Description

Site isolation issue in the Audio/Video: Web Codecs 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 — fixed in 153.1.0
Mozilla Thunderbird: before 153.1.0 — fixed in 153.1.0

How to fix

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

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2050480
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/

Get alerted when CVE-2026-74981 or the next vulnerability affects your stack