CVE-2026-6776 Mozilla CVE debrief

Who should care

Defenders responsible for managing and securing Mozilla Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR installations should assess exposure and apply patches to mitigate potential risks.

Why it matters

CVE-2026-6776 is a HIGH severity vulnerability in Mozilla Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR due to incorrect boundary conditions in the WebRTC: Networking component. Defenders should prioritize verifying and applying patches to mitigate potential risks.

• Verify and apply patches to prevent potential exploitation.
• Inventory and update affected versions to fixed versions.
• Monitor for exploitation attempts targeting this vulnerability.

Technical summary

The vulnerability is caused by incorrect boundary conditions in the WebRTC: Networking component of Mozilla Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR. This issue was addressed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10. The WebRTC: Networking component handles network communication for WebRTC, and the incorrect boundary conditions could allow for potential exploitation. Defenders should prioritize verifying and applying the provided patches to mitigate potential risks associated with this vulnerability.

Defensive priority

Defenders should prioritize verifying and applying the provided patches to mitigate potential risks associated with this vulnerability.

Recommended defensive actions

• Verify and apply patches for Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR to the latest versions.
• Inventory checks for affected versions and update to fixed versions (Firefox 150, Firefox ESR 140.10, Thunderbird 150, Thunderbird 140.10).
• Monitor for potential exploitation attempts targeting this vulnerability.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance.
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.
• Review compensating controls for exposed systems while remediation is scheduled and verified.

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its CVSS score, affected products, and fixed versions. The vulnerability was publicly disclosed on 2026-04-21 and has not been modified since then. The CVE record and NVD entry serve as the primary sources of information for this vulnerability. Defenders should verify the affected products and apply patches accordingly. The evidence is limited to publicly available information, and defenders should be aware of potential unknown affected scope.

Sources and 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.