NLTK (Natural Language Toolkit) before version 3.9.3 contains an eval injection vulnerability in the nltk.collocations module that allows an attacker who controls command-line arguments to execute arbitrary Python code. When collocations.py is invoked directly, the __main__ block passes command-line arguments directly to eval() as suffixes of BigramAssocMeasures without allowlist validation or sanitization, enabling an attacker to supply a Python expression that escapes the intended attribute lookup and executes arbitrary code including OS commands via the os module.
Fix
Patch, vendor advisory and mitigation references on NVD 3
- https://github.com/nltk/nltk/commit/66f14096d952ec8f04934f515e027534bd4eb0ac Patch
- https://github.com/nltk/nltk/pull/3465 Issue Tracking, Patch
- https://www.vulncheck.com/advisories/nltk-eval-injection-via-collocations-py-command-line-arguments Patch, Third Party Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 8.5 · nltkNVD modified 2026-10-08 16:16
Affected (CPE criteria) 1
cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*
References 5
- https://aydinnyunus.github.io/2026/06/07/command-injection-nltk-collocations-eval/ Exploit, Press/Media Coverage, Third Party Advisory
- https://github.com/nltk/nltk/commit/66f14096d952ec8f04934f515e027534bd4eb0ac Patch
- https://github.com/nltk/nltk/pull/3465 Issue Tracking, Patch
- https://github.com/nltk/nltk/releases/tag/3.9.3 Release Notes
- https://www.vulncheck.com/advisories/nltk-eval-injection-via-collocations-py-command-line-arguments Patch, Third Party Advisory