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Advisory details: pypa / nltk/PYSEC-2026-3657
Advisory ID pypa/nltk/PYSEC-2026-3657
Aliases CVE-2025-71408
GHSA-848c-c2cx-j7qx
PYSEC-2026-3657
Summary 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.
Status Published
Exploitability 0.5
Weighted Severity 7.7
Risk 3.9
Affected and Fixed Packages Package Details
Introduced and Fixed Package Commit Patches Package Commit Patches Details
Weaknesses (0)
There are no known CWE.
System Score Found at
cvssv4 8.5 https://github.com/pypa/advisory-database/blob/main/vulns/nltk/PYSEC-2026-3657.yaml
Reference id Reference type URL
https://aydinnyunus.github.io/2026/06/07/command-injection-nltk-collocations-eval/
https://github.com/advisories/GHSA-848c-c2cx-j7qx
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
No exploits are available.

No EPSS data available for this advisory.

Patch URL
There are no known patches.
Vector: 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 Found at https://github.com/pypa/advisory-database/blob/main/vulns/nltk/PYSEC-2026-3657.yaml
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

low

high

none

present

none

low

high

none

passive

active

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

Vector: SSVCv2/E:P/A:N/T:T/P:M/B:A/M:M/D:R/2026-07-27T17:22:32Z/

Decision: Track*

Source URL: https://github.com/cisagov/vulnrichment/blob/develop/2025/71xxx/CVE-2025-71408.json

Source Advisory: vulnrichment/CVE-2025-71408

View SSVC decision tree 
[{'Exploitation': 'poc'},
 {'Automatable': 'no'},
 {'Technical Impact': 'total'},
 {'Mission Prevalence': 'minimal'},
 {'Public Well-being Impact': 'material'},
 {'Mission & Well-being': 'medium'}]