parser3-cgi and libapache2-mod-parser3 combine GPL licensed files with the RSA-MD licensed files in src/lib/md5.
RSA-MD is incompatible with any GPL version because of its advertisement clause:
"""
License is also granted to make and use derivative works provided that such works are identified as "derived from the RSA Data
Security, Inc. MD5 Message-Digest Algorithm" in all material mentioning or referencing the derived work.
"""
Also, the Apache-1.1 license used in those files is problematic with GPL.