What’s Vulnerable › Vulnerabilities

CVE-2026-100819: Sandbox escape due to incorrect boundary conditions in the XPCOM component

• Severity: critical (CVSS 9.6 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-29 · updated 2026-10-05
• Weakness: CWE-119

Description

Sandbox escape due to incorrect boundary conditions in the XPCOM component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.

Affected products

• Mozilla Firefox: before 115.42.0; from 116.0 before 140.17.0; from 141.0 before 153.4.0; from 154.0.0 before 157.0.0 — fixed in 115.42.0, 140.17.0, 153.4.0, 157.0.0
• Mozilla Thunderbird: before 140.17.0; from 141.0 before 153.4.0; from 154.0 before 157.0 — fixed in 140.17.0, 153.4.0, 157.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.42.0, 140.17.0, 153.4.0, 157.0.0; Mozilla Thunderbird 140.17.0, 153.4.0, 157.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2071069
• https://www.mozilla.org/security/advisories/mfsa2026-100/
• https://www.mozilla.org/security/advisories/mfsa2026-101/
• https://www.mozilla.org/security/advisories/mfsa2026-102/
• https://www.mozilla.org/security/advisories/mfsa2026-103/
• https://www.mozilla.org/security/advisories/mfsa2026-97/
• https://www.mozilla.org/security/advisories/mfsa2026-98/
• https://www.mozilla.org/security/advisories/mfsa2026-99/

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