CVE-2026-81727: NLTK: Downloader.download follows hardlinks and overwrites outside-root files
NLTK’s downloader now blocks symlink escapes during ZIP extraction, but it still treats pre-existing hardlinks inside the install tree as ordinary in-root files. A normal package install can therefore overwrite an outside-root inode through that hardlink.
References
- github.com/advisories/GHSA-f794-5jv7-7672
- github.com/nltk/nltk/commit/9e6d5f05902b9aaa1221a0a565448d17a9c9b3e8
- github.com/nltk/nltk/pull/3797
- github.com/nltk/nltk/releases/tag/v3.10.3
- github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672
- github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3741.yaml
- nvd.nist.gov/vuln/detail/CVE-2026-81727
- www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader
Code Behaviors & Features
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