Mateusz Sionkowski

**Name of the Vulnerable Software and Affected Versions** Firefox versions prior to 100 Firefox ESR versions prior to 91.9 Thunderbird versions prior to 91.9 **Description** The issue is related to insufficient protection of internal data when handling CSS variables, which could allow a remote attacker to access protected information or have other impacts. This vulnerability can be used to probe the browser history by exploiting the different behavior of browsers when loading CSS resources involving CSS variables. **Recommendations** For Firefox versions prior to 100, update to version 100 or later. For Firefox ESR versions prior to 91.9, update to version 91.9 or later. For Thunderbird versions prior to 91.9, update to version 91.9 or later.