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: nltk
References5
- github.com/nltk/nltk/commit/66f14096d952ec8f04934f515e027534bd4… Patch
- github.com/nltk/nltk/pull/3465 Issue TrackingPatch
- www.vulncheck.com/advisories/nltk-eval-injection-via-collocatio… PatchThird Party Advisory
- aydinnyunus.github.io/2026/06/07/command-injection-nltk-colloca… ExploitPress/Media CoverageThird Party Advisory
- github.com/nltk/nltk/releases/tag/3.9.3 Release Notes
Metrics
- CVSS 3.1
-
7.8
HIGH
Score source: CNA
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H - CVSS 4.0
-
8.5
HIGH
Score source: CNA
CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 19 · as of 14 November 2026
- CWE
- CWE-95
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.