CVE-2026-78683

CRITICAL 9.6

NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization

CVSS Score

9.6

EPSS Score

0.0%

EPSS Percentile

0th

NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/parse/transitionparser.py). The method calls pickle_load() with the default restricted=False, routing deserialization through WarningUnpickler, which does not override find_class() and therefore permits arbitrary class resolution. When an application loads an attacker-crafted model file, embedded pickle gadget chains execute arbitrary Python code with the privileges of the user running the application. NLTK provides a RestrictedUnpickler for safe deserialization, but it is not used by production code paths. Fixed in 3.10.0.

CWE	CWE-502
Vendor	nltk
Product	nltk
Published	Aug 25, 2026

Stay Ahead of the Next One

Get instant alerts for nltk nltk

Be the first to know when new critical vulnerabilities affecting nltk nltk are published — delivered to Slack, Telegram or Discord.

Get Free Alerts → Free · No credit card · 60 sec setup

CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Affected Versions

nltk / nltk

0 < 3.10.0

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2 vulncheck.com: https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization

Credits

ekaf