CVE-2026-100778: mozilla firefox, mozilla thunderbird

CVSS 9.6 (critical) · published 2026-09-29

Sandbox escape due to use-after-free in the DOM: Core & HTML 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 (NVD): mozilla firefox, mozilla thunderbird

Fixed in (NVD): 115.42.0, 140.17.0, 153.4.0, 157.0.0, 157.0

Weakness: CWE-416

Source: NVD CVE-2026-100778

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2068406
• 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/

Check your software

Connect an AI agent to the Fixlane MCP server or ask the Telegram bot to check what you have installed against incidents with a verified fixed version.