CVE-2025-71408: nltk Eval Injection

Vulnerability summary

CVE-2025-71408 is a high (CVSS 8.5) Eval Injection vulnerability in nltk. EPSS estimates a 0.27% chance of exploitation in the next 30 days, higher than 17.3% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 24-07-2026
   PublishedVulnerability first disclosed.
2. 08-10-2026
   Last modifiedVulnerability information updated.

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.

• CWE-95Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection')The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes code syntax before using the input in a dynamic evaluation call (e.g. "eval").