There are 2 open security issues in bullseye.
2 issues left for the package maintainer to handle:
A flaw was found in the copying tool `nbdcopy` of libnbd. When performing multi-threaded copies using asynchronous nbd calls, nbdcopy was blindly treating the completion of an asynchronous command as successful, rather than checking the *error parameter. This could result in the silent creation of a corrupted destination image.
A flaw was found in libnbd 1.7.3. An assertion failure in nbd_unlocked_opt_go in ilb/opt.c may lead to denial of service.
You can find information about how to handle these issues in the security team's documentation.