CVE-2026-4690: Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component

Severity: high (CVSS 8.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-24 · updated 2026-07-15
Weakness: CWE-190

Description

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.

Affected products

Mozilla Firefox: before 115.34.0; before 149.0; from 128.0 before 140.9.0 — fixed in 115.34.0, 140.9.0, 149.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.34.0, 140.9.0, 149.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2016375
https://www.mozilla.org/security/advisories/mfsa2026-20/
https://www.mozilla.org/security/advisories/mfsa2026-21/
https://www.mozilla.org/security/advisories/mfsa2026-22/
https://www.mozilla.org/security/advisories/mfsa2026-23/
https://www.mozilla.org/security/advisories/mfsa2026-24/
https://access.redhat.com/errata/RHSA-2026:5930
https://access.redhat.com/errata/RHSA-2026:5931
https://access.redhat.com/errata/RHSA-2026:5932
https://access.redhat.com/errata/RHSA-2026:6188
https://access.redhat.com/errata/RHSA-2026:6342
https://access.redhat.com/errata/RHSA-2026:6917

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