Privilege Escalation in Firefox and Firefox ESR by Mozilla
CVE-2026-2777

9.8CRITICAL

Key Information:

Vendor

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

What is CVE-2026-2777?

A vulnerability in the Messaging System component of Mozilla's Firefox allows for privilege escalation, impacting users on certain versions of both standard Firefox and Firefox ESR. This flaw could potentially enable unauthorized access or manipulation of system resources, affecting overall application security. Users are urged to update to the latest versions to mitigate any risks associated with this vulnerability.

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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=2015305
https://www.mozilla.org/security/advisories/mfsa2026-13/
https://www.mozilla.org/security/advisories/mfsa2026-14/

CVSS V3.1

Score:
9.8
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Richard Belisle
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