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CVE-2026-4697 Mozilla CVE debrief

CVE-2026-4697 is a HIGH severity vulnerability in Mozilla Firefox, Thunderbird, and Firefox ESR. It relates to incorrect boundary conditions in the Audio/Video: Web Codecs component. This issue was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9. The vulnerability was publicly disclosed on March 24, 2026, and last modified on June 30, 2026. The CVSS score for this vulnerability is 7.5.

Vendor
Mozilla
Product
Firefox
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-03-24
Original CVE updated
2026-07-15
Advisory published
2026-03-24
Advisory updated
2026-07-15

Who should care

Organizations and individuals using Mozilla Firefox, Thunderbird, or Firefox ESR should prioritize patching this vulnerability. Given its HIGH severity and potential for exploitation, defenders should ensure that all users have updated to the patched versions. This vulnerability could be particularly concerning for organizations with high-risk exposure to web-based attacks.

Technical summary

The vulnerability, CVE-2026-4697, is caused by incorrect boundary conditions in the Audio/Video: Web Codecs component of Mozilla Firefox, Thunderbird, and Firefox ESR. This issue allows for potential crashes and potentially exploitable situations. The Common Vulnerabilities and Exposures (CVE) score for this issue is 7.5, indicating a HIGH severity level. The vulnerability was addressed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9. The CVSS vector for this vulnerability is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Defensive priority

Defenders should prioritize patching CVE-2026-4697 due to its HIGH severity and potential for exploitation. Ensure all instances of Mozilla Firefox, Thunderbird, and Firefox ESR are updated to the patched versions: Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Recommended defensive actions

  • Update Mozilla Firefox to version 149 or later.
  • Update Mozilla Firefox ESR to version 140.9 or later.
  • Update Mozilla Thunderbird to version 149 or later.
  • Update Mozilla Thunderbird to version 140.9 or later.
  • Verify that all users have updated to the patched versions.

Evidence notes

The CVE-2026-4697 vulnerability details were obtained from the official CVE record and the National Vulnerability Database (NVD). The CVE was publicly disclosed on March 24, 2026, and last modified on June 30, 2026. The vulnerability affects multiple Mozilla products, including Firefox, Thunderbird, and Firefox ESR. The CVSS score for this vulnerability is 7.5, indicating a HIGH severity level.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-4697 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-4697

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-4697 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-4697

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.