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.
Attack Parameters
Attack Vector
Local
Requires local access
Attack Complexity
Low
Easy to exploit
Attack Requirements
None
No additional conditions
Privileges Required
Low
Basic privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
High
Complete data leak
Integrity
High
Complete data modification
Availability
High
Complete denial of service
CVSS Vector v4.0
Weakness Type (CWE)
References 5
https://aydinnyunus.github.io/2026/06/07/command-injection-nltk-collocations-ev…
disclosure@vulncheck.com
https://github.com/nltk/nltk/commit/66f14096d952ec8f04934f515e027534bd4eb0ac
disclosure@vulncheck.com
https://github.com/nltk/nltk/pull/3465
disclosure@vulncheck.com
https://github.com/nltk/nltk/releases/tag/3.9.3
disclosure@vulncheck.com
https://www.vulncheck.com/advisories/nltk-eval-injection-via-collocations-py-co…
disclosure@vulncheck.com