CVE-2026-79676

### Summary Several corpus readers still step outside NLTK's symlink-aware trusted-root model. They derive in-root paths from trusted corpus state, convert those paths back into plain strings, and reopen them with built-in `open()` rather than `nltk.pathsec.open()`. ### Details - **Vulnerability type:** Path traversal and symlink boundary bypass - **Affected component:** `nltk.corpus.reader.ipipan`, `nltk.corpus.reader.crubadan`, `nltk.corpus.reader.lin` - **Affected versions:** Published `3.9.4` and current source `v3.10.0-rc2` both reproduced. - **Patched versions:** Not yet patched - **Root cause:** Root-derived paths are reopened with raw `open()` without preserving the trusted-root boundary. `IPIPANCorpusReader` opens `header.xml` derived from `morph.xml`, `CrubadanCorpusReader` opens `table.txt` directly, and `LinThesaurusCorpusReader` opens `simN.lsp` paths returned from its own root helpers. Under `pathsec.ENFORCE=True`, a symlink placed inside the trusted corpus root can point outside the root and still be parsed successfully. It was confirmed parsed outside-root content is returned through public methods such as `channels()`, `domains()`, `categories()`, `langs()`, `crubadan_to_iso()`, `synonyms()`, and `scored_synonyms()`. ### PoC **Preconditions** - The application processes attacker-influenced corpora inside a trusted NLTK data root or trusted corpus directory. **Steps** 1. Create a trusted corpus root and keep `pathsec.ENFORCE=True` with that root allowlisted. 2. Place symlinked reader inputs such as `header.xml`, `table.txt`, or `simN.lsp` inside the root and point them to external files. 3. Instantiate the corresponding corpus reader and call its normal public methods. 4. Observe that parsed outside-root values are returned even though `pathsec.open()` blocks the same symlink targets. **Minimal reproducible excerpt** ```text {'ipipan': ['LEAK', 'TOPSECRET', 'CLASSIFIED'], 'crubadan': ['LEAK'], 'lin': [('LEAK', 9.5)]} ``` ### Impact An atta