CVE-2026-74986

Name of the Vulnerable Software and Affected Versions Firefox versions prior to 154 Firefox ESR versions prior to 153.1 Thunderbird versions prior to 154 Thunderbird versions prior to 153.1

Description A site isolation issue exists within the CSS Parsing and Computation component. Site isolation is a security mechanism that ensures web pages from different sites are processed in separate processes to prevent data leakage.

Recommendations Update Firefox to version 154. Update Firefox ESR to version 153.1. Update Thunderbird to version 154. Update Thunderbird to version 153.1.