CVE-2025-71408
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.20%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 4.0
- 8.5 HIGHCVSS: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/M
- EPSS
- 0.20% probability · 10th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-95
- Affected
- nltk/nltk
- Source
- disclosure@vulncheck.com
References
- https://aydinnyunus.github.io/2026/06/07/command-injection-nltk-collocations-eval/Exploit, Press/Media Coverage, Third Party Advisory
- https://github.com/nltk/nltk/commit/66f14096d952ec8f04934f515e027534bd4eb0acPatch
- https://github.com/nltk/nltk/pull/3465Issue Tracking, Patch
- https://github.com/nltk/nltk/releases/tag/3.9.3Release Notes
- https://www.vulncheck.com/advisories/nltk-eval-injection-via-collocations-py-command-line-argumentsPatch, Third Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.