There are 2 open security issues in bullseye.
2 issues left for the package maintainer to handle:
zlib before 1.2.12 allows memory corruption when deflating (i.e., when compressing) if the input has many distant matches.
zlib through 1.2.12 has a heap-based buffer over-read or buffer overflow in inflate in inflate.c via a large gzip header extra field. NOTE: only applications that call inflateGetHeader are affected. Some common applications bundle the affected zlib source code but may be unable to call inflateGetHeader (e.g., see the nodejs/node reference).
You can find information about how to handle these issues in the security team's documentation.