CVE-2026-62383: NLTK: Symlink-based arbitrary file read in IPIPANCorpusReader, bypasses nltk.pathsec entirely

IPIPANCorpusReader (nltk/corpus/reader/ipipan.py) exposes public methods, channels(), domains(), categories(), and fileids(channels=...), that accept a caller supplied fileids list and read a file via a completely unprotected builtin open() call, with no nltk.pathsec involvement at all. A symlink placed inside the corpus root, with a name containing no separators or .., passes NLTK’s existing traversal checks and is opened directly, reading a file from anywhere on the filesystem the process can access.