GHSA-83pf-v6qq-pwmr: Fickling has a detection bypass via stdlib network-protocol constructors

Fickling is a tool that checks whether pickle files (serialized Python objects) are safe to open. Researchers found that Fickling incorrectly marked dangerous pickle files as safe when they used network protocol constructors like SMTP, IMAP, FTP, POP3, Telnet, and NNTP, which establish outbound TCP connections during deserialization. The vulnerability has two causes: an incomplete blocklist of unsafe imports, and a logic flaw in the unused variable detector that fails to catch suspicious code patterns.