CVE-2026-84121

Name of the Vulnerable Software and Affected Versions Firefox versions prior to 155 Firefox ESR versions prior to 115.40 Firefox ESR versions prior to 140.15 Firefox ESR versions prior to 153.2 Thunderbird versions prior to 155 Thunderbird versions prior to 140.15 Thunderbird versions prior to 153.2

Description A use-after-free issue exists in the DOM: Security component, which can lead to a sandbox escape. A use-after-free is a memory corruption flaw that occurs when an application continues to use a pointer after it has been freed.

Recommendations Update Firefox to version 155. Update Firefox ESR to version 115.40. Update Firefox ESR to version 140.15. Update Firefox ESR to version 153.2. Update Thunderbird to version 155. Update Thunderbird to version 140.15. Update Thunderbird to version 153.2.