Remote Code Execution Vulnerability in NLTK by NLTK
CVE-2026-79657

9.3CRITICAL

Key Information:

Vendor

Nltk

Status
Nltk
Vendor
CVE Published:
25 August 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2026-79657?

Versions of NLTK prior to 3.10.3 include a significant remote code execution vulnerability that arises from their handling of allowlisted pickle loaders. These loaders trust entire module namespaces instead of restricting access to specific safe callables. This flaw allows attackers to craft malicious pickle payloads that can invoke potentially harmful functions from the namespace during the loading of model or tokenizer artifacts. Notably, functions like ReppTokenizer._execute and numpy.f2py.crackfortran.myeval can be exploited through the pickle REDUCE, enabling arbitrary command execution.

Affected Version(s)

nltk 0 < 3.10.3

nltk 3.10.3

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

cortex9-nltk-pickle-allowlist-prefix-model
Created by federiconbaez

References

https://github.com/nltk/nltk/security/advisories/GHSA-x99...
vendor-advisory
https://www.vulncheck.com/advisories/nltk-before-3.10.3-r...
third-party-advisory

CVSS V4

Score:
9.3
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

leduckhuong
.