Sandbox Escape Vulnerability in Firefox and Firefox ESR
CVE-2026-2776

10CRITICAL

Key Information:

Vendor

Mozilla
Status
Firefox
Firefox Esr
Thunderbird
Vendor
CVE Published:
24 February 2026

What is CVE-2026-2776?

This vulnerability allows for a potential sandbox escape through improper boundary condition handling in the Telemetry component of Firefox and its Extended Support Release (ESR). Affected versions are Firefox prior to 148, and Firefox ESR versions earlier than 115.33 and 140.8. Exploiting this vulnerability could permit unauthorized access to sensitive data and the execution of potentially harmful commands outside the intended security constraints.

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Affected Version(s)

Firefox < 148

Firefox ESR < 115.33

Firefox ESR < 140.8

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2015266
https://www.mozilla.org/security/advisories/mfsa2026-13/
https://www.mozilla.org/security/advisories/mfsa2026-14/

CVSS V3.1

Score:
10
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Changed

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Sajeeb Lohani
JSON
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