[GHSA] GHSA-r6gq-whwq-mvg9 (high) — NLTK: Symlink escape in CorpusReader allows arbitrary local file read outside the corpus root

GHSA-r6gq-whwq-mvg9 Severity: high CVE: CVE-2026-70626

NLTK: Symlink escape in CorpusReader allows arbitrary local file read outside the corpus root

### Summary `nltk.corpus.reader.api.CorpusReader.open()` can be used to read files outside the intended corpus root via a symlink placed inside that root. Although NLTK blocks absolute paths and `..` traversal, the current boundary check is only lex