What’s Vulnerable › Vulnerabilities

CVE-2025-71408: NLTK < 3.9.3 Eval Injection via collocations.py Command-Line Arguments

• Severity: high (CVSS 7.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-07-24 · updated 2026-10-08
• Weakness: CWE-95

Description

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.

Affected products

• nltk: before 3.9.3 — fixed in 3.9.3

How to fix

Upgrade to a fixed version: nltk 3.9.3. Check the vendor advisory for mitigations.

References

• https://aydinnyunus.github.io/2026/06/07/command-injection-nltk-collocations-eval/
• https://github.com/nltk/nltk/commit/66f14096d952ec8f04934f515e027534bd4eb0ac
• https://github.com/nltk/nltk/pull/3465
• https://github.com/nltk/nltk/releases/tag/3.9.3
• https://www.vulncheck.com/advisories/nltk-eval-injection-via-collocations-py-command-line-arguments

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