CVE-2026-2776 Mozilla CVE debrief

Who should care

Organizations and individuals using Mozilla Firefox, Firefox ESR, Thunderbird, or Thunderbird ESR should prioritize patching this vulnerability to prevent potential sandbox escapes. This vulnerability is particularly concerning due to its critical severity and potential for exploitation. Users of Red Hat products may also be affected, as indicated by multiple Red Hat errata references.

Technical summary

The CVE-2026-2776 vulnerability is caused by incorrect boundary conditions in the Telemetry component of Mozilla Firefox. This flaw allows for a sandbox escape, which could potentially be used by attackers to execute arbitrary code or access sensitive data. The vulnerability affects multiple products, including Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR. The CVSS vector for this vulnerability is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H, indicating a high level of exploitability and potential impact.

Defensive priority

This vulnerability should be prioritized for immediate patching due to its critical severity and potential for exploitation. Organizations should ensure that all affected systems and users are updated to the latest patched versions of Firefox, Firefox ESR, Thunderbird, or Thunderbird ESR.

Recommended defensive actions

• Apply patches for Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
• Ensure all affected systems and users are updated to the latest patched versions.
• Review and update vulnerability management processes to ensure timely patching of critical vulnerabilities.
• Monitor for potential exploitation attempts using security monitoring tools.
• Verify that compensating controls are in place for unpatched systems, if necessary.

Evidence notes

The CVE-2026-2776 vulnerability is well-documented in multiple sources, including the official CVE record, NVD detail page, and various vendor advisories. The vulnerability has a high level of confidence due to its critical severity and multiple references. However, the exact scope of affected systems and potential exploitation attempts are not explicitly stated in the provided sources.

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.