There are 2 open security issues in bullseye.
1 issue left for the package maintainer to handle:
A flaw was found in Cockpit in versions prior to 260 in the way it handles the certificate verification performed by the System Security Services Daemon (SSSD). This flaw allows client certificates to authenticate successfully, regardless of the Certificate Revocation List (CRL) configuration or the certificate status. The highest threat from this vulnerability is to confidentiality.
You can find information about how to handle this issue in the security team's documentation.
1 ignored issue:
Cockpit (and its plugins) do not seem to protect itself against clickjacking. It is possible to render a page from a cockpit server via another website, inside an <iFrame> HTML entry. This may be used by a malicious website in clickjacking or similar attacks.