Bug 2523216 (CVE-2026-78683)

Summary:	CVE-2026-78683 nltk: NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	anpicker, bparees, dschmidt, ebourniv, hasun, ikhan, jfula, jlanda, jowilson, kshier, nyancey, ometelka, ptisnovs, rbobbitt, sbunciak, simaishi, stcannon, syedriko, xdharmai, yguenane
Target Milestone:	---	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in NLTK. This vulnerability allows arbitrary code execution due to unsafe deserialization, where data loaded from storage is converted back into active objects without adequate restrictions. When the TransitionParser component processes a model file, it fails to enforce safe loading constraints. An attacker who provides a maliciously crafted model file can trigger the execution of arbitrary code with the permissions of the user or application running NLTK.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2542499, 2542500
Bug Blocks:

Description OSIDB Bzimport 2026-08-25 01:53:53 UTC

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.