CVE-2026-109759

Name of the Vulnerable Software and Affected Versions Firefox versions prior to 158 Firefox ESR versions prior to 153.5 Thunderbird versions prior to 158 Thunderbird versions prior to 153.5

Description A site isolation issue exists within the Networking component. Site isolation is a security mechanism that ensures web pages from different sites are processed in separate processes to prevent one site from accessing data from another.

Recommendations Update Firefox to version 158 or later. Update Firefox ESR to version 153.5 or later. Update Thunderbird to version 158 or later. Update Thunderbird to version 153.5 or later.