CVE-2026-4687: Sandbox escape due to incorrect boundary conditions in the Telemetry component

Severity: high (CVSS 8.6 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% 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-754

Description

Sandbox escape due to incorrect boundary conditions in the Telemetry 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=2016368
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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