Aegisub executes arbitrary code through automatically loaded Automation scripts

Aegisub is a cross-platform advanced subtitle editor. From 3.2.0 to 3.4.2, Aegisub automatically loads Automation scripts referenced by `Automation Scripts` metadata in `ASS` subtitle projects without asking whether the user trusts the scripts or their authors. An attacker can distribute a crafted `ASS` file together with a referenced malicious Automation script, and opening the `AS`  file executes arbitrary code with the privileges of the Aegisub process. From 3.4.0 to 3.4.2, inconsistent handling of embedded `NUL` characters between extension validation and filesystem operations additionally allows a crafted `ASS/Lua` polyglot to reference and execute itself as a single-file variant. The vulnerability is fixed in Aegisub 3.5.0.