Vulnerability details

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.

• https://aydinnyunus.github.io/2026/06/07/command-injection-nltk-collocations-eval/ technical-descriptionexploit
• https://github.com/nltk/nltk/releases/tag/3.9.3 release-notespatch
• https://github.com/nltk/nltk/pull/3465 issue-trackingpatch
• https://github.com/nltk/nltk/commit/66f14096d952ec8f04934f515e027534bd4eb0ac patch
• https://www.vulncheck.com/advisories/nltk-eval-injection-via-collocations-py-command-line-arguments third-party-advisory