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CVE-2026-78683 Details

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.

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:9.6 CRITICALVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2	CISA-ADP	ExploitVendor Advisory
https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2	[email protected]	ExploitVendor Advisory
https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization	[email protected]	Third Party Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-502	Deserialization of Untrusted Data	[email protected]

Affected Products

Product	Versions
nltk nltk	< 3.10.0
CPE cpe:2.3:a:nltk:nltk:::::::: Remediation No remediation found in references.

Change History

3 change records found show changes

Date	Action	Recorded By
Aug 31, 2026	Initial Analysis	[email protected]
Aug 25, 2026	CVE Modified	CISA-ADP
Aug 25, 2026	New CVE Received	[email protected]