CVE-2026-4689

moderate-risk

Published 2026-03-24

Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Do I need to act?

0.03% chance of exploitation

EPSS score — low exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 10.0/10 Critical

NETWORK / LOW complexity

Affected Products (4)

Firefox

Thunderbird

Affected Vendors

Mozilla

References (6)

Permissions Required https://bugzilla.mozilla.org/show_bug.cgi?id=2016374

Vendor Advisory https://www.mozilla.org/security/advisories/mfsa2026-20/

Vendor Advisory https://www.mozilla.org/security/advisories/mfsa2026-21/

Vendor Advisory https://www.mozilla.org/security/advisories/mfsa2026-22/

Vendor Advisory https://www.mozilla.org/security/advisories/mfsa2026-23/

Vendor Advisory https://www.mozilla.org/security/advisories/mfsa2026-24/

/ 100

moderate-risk

Severity 33/34 · Critical

Exploitability 0/34 · Minimal

Exposure 10/34 · Low