Boundary Condition Flaw in Firefox Affects multiple Versions
CVE-2026-4699

7.5HIGH

Key Information:

Vendor

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

What is CVE-2026-4699?

A vulnerability exists in Firefox's Layout: Text and Fonts component due to incorrect boundary conditions, potentially leading to unintended behavior or exposure of sensitive information. This issue affects several Firefox versions, including those prior to 149, and designated Extended Support Releases (ESR) below 115.34 and 140.9, necessitating immediate attention to ensure user safety.

Affected Version(s)

Firefox < 149

Firefox ESR < 115.34

Firefox ESR < 140.9

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2021863
https://www.mozilla.org/security/advisories/mfsa2026-20/
https://www.mozilla.org/security/advisories/mfsa2026-21/

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Matej Smycka
.