CVE-2026-4695: Mozilla Firefox and Thunderbird incorrect boundary conditions in Web Codecs

CVE-2026-4695 · Severity: high · CVSS 7.5 · Published 2026-03-24

A vulnerability exists in the web browser and email client components responsible for processing audio and video content. An attacker could exploit this flaw to cause the application to crash or become unresponsive, potentially disrupting business operations and user productivity. This issue affects users of Firefox and Thunderbird who have not yet updated to the latest security releases.

Technologies: Mozilla Firefox, Mozilla Firefox ESR, Mozilla Thunderbird, Mozilla Thunderbird ESR, Red Hat Enterprise Linux AppStream EUS. Vendors: Mozilla, Red Hat.

Quick answers

Is CVE-2026-4695 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-4695 being exploited in the wild.
How severe is CVE-2026-4695?
High severity, with a CVSS score of 7.5, published 24 March 2026.
Which products and versions are affected?
Mozilla Firefox < 149; Mozilla Firefox ESR < 140.9; Mozilla Thunderbird < 149; Mozilla Thunderbird ESR < 140.9; and 1 more.
Is there a fix for CVE-2026-4695?
A patch was published on 2026-03-24: Fixed in Firefox 149 and Firefox ESR 140.9 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-4695 attacked?
It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-4695?
Check whether you run Mozilla Firefox, Mozilla Firefox ESR, Mozilla Thunderbird or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

This vulnerability is classified as an improper check for unusual or exceptional conditions (CWE-754) and incorrect calculation of buffer size (CWE-131) within the Web Codecs component of the Audio/Video subsystem. The flaw is triggered by incorrect boundary conditions during media processing. A remote, unauthenticated attacker can exploit this over the network to cause a denial-of-service (application crash). The vulnerability was addressed by improving boundary checks in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Affected products

  • Mozilla Firefox < 149
  • Mozilla Firefox ESR < 140.9
  • Mozilla Thunderbird < 149
  • Mozilla Thunderbird ESR < 140.9
  • Red Hat Enterprise Linux Server (v. 7 ELS) 7
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) 10.0

Timeline

  • 2026-03-24: advisory: Mozilla Foundation Security Advisory published
  • 2026-03-24: patched: Fixed in Firefox 149 and Firefox ESR 140.9

References

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