CVE-2026-78683

NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization

Published: Aug 25, 2026Updated: Aug 31, 2026 Sources: CVE List NVDCWE-502

9.6CRITICAL

Description

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.

No summary for this CVE yet.

CVSS Vector Breakdown

Exploitability

AV:NAttack Vector

Network

AC:LAttack Complexity

Low

PR:NPrivileges Required

None

UI:RUser Interaction

Required

Scope

S:CScope

Changed

Impact

C:HConfidentiality

High

I:HIntegrity

High

A:HAvailability

High

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Weaknesses

CWE-502

Affected Products

nltk

oss-projectaka nltk/nltk

nltkLibrary

AI / ML / ml-framework

Exploitability

Official Patch Available

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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

3 techniques

Execution

Initial Access

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References

https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2

github.com

https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization

vulncheck.com

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