Vulnerability · Published Jul 24, 2026 · Assigned by VulnCheck

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

High 7.8

In plain English

A high-severity security flaw in ntlk from ntlk. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 19% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.8High

Exploit odds (30 days)0.3%top 81.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	nltk	no fix listed	DEBIAN-CVE-2025-71408
Debian:13	nltk	no fix listed	DEBIAN-CVE-2025-71408
Debian:14	nltk	3.9.3-1	DEBIAN-CVE-2025-71408
PyPI	nltk	3.9.3	GHSA-848c-c2cx-j7qx
PyPI	nltk	3.9.3	PYSEC-2026-3657

Affected products (as reported)

Vendor	Product	Versions
ntlk	ntlk	0 – before 3.9.3

Weakness: CWE-95 · Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

References

Researcher Disclosure technical-description, exploit
NLTK 3.9.3 Release Notes release-notes, patch
Pull Request issue-tracking, patch
Patch Commit patch
https://www.vulncheck.com/advisories/nltk-eval-injection-via-collocations-py-command-line-arguments third-party-advisory