systemd 250 and 251 allows local users to achieve a systemd-coredump deadlock by triggering a crash that has a long backtrace. This occurs in parse_elf_object in shared/elf-util.c. The exploitation methodology is to crash a binary calling the same function recursively, and put it in a deeply nested directory to make its backtrace large enough to cause the deadlock. This must be done 16 times when MaxConnections=16 is set for the systemd/units/systemd-coredump.socket file.
https://github.com/systemd/systemd/pull/25055#issuecomment-1313733553
https://github.com/systemd/systemd/pull/24853#issuecomment-1326561497
https://github.com/systemd/systemd/commit/076b807be472630692c5348c60d0c2b7b28ad437