CVE-2026-70626: NLTK before 3.9.4 Symlink Escape via CorpusReader

Severity: medium (CVSS 6.2 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-08-22 · updated 2026-10-14
Weakness: CWE-59

Description

NLTK versions before 3.9.4 contain a symlink escape vulnerability in CorpusReader.open() that allows local attackers to read arbitrary files outside the corpus root. The vulnerability exists because path validation is lexical and does not account for symlink resolution, enabling attackers to place symlinks inside the corpus root to access files outside the intended boundary.

Affected products

nltk: before 3.9.4 — fixed in 3.9.4

How to fix

Upgrade to a fixed version: nltk 3.9.4. Check the vendor advisory for mitigations.

References

https://github.com/nltk/nltk/security/advisories/GHSA-r6gq-whwq-mvg9
https://www.vulncheck.com/advisories/nltk-before-symlink-escape-via-corpusreader
https://github.com/nltk/nltk/security/advisories/GHSA-r6gq-whwq-mvg9

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