The vulnerability of the Thunderbird email client and the Firefox ESR browser lies in a error during the processing of CSS style sheets accessible through internal URIs, such as “resource:”. This allows attackers to circumvent the implemented content security policies.

The vulnerability of the Thunderbird email client and the Firefox ESR browser is related to an error in processing CSS style sheets that are accessed through internal URIs, as “resource:”. Exploiting this vulnerability can allow a malicious actor to bypass implemented content security policies...