CVE WatchAug 31, 2026

CVE-2026-78683

NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() metho

CVSS

9.6

Critical

EPSS

0.3%

p21

KEV

—

Exploit Today

0-100

Published: Aug 25, 2026 · Last modified: Aug 31, 2026 · CWE-502

EPSS · 30d

0.3%EPSS · 30 days0.3%

2026-08-252026-09-06

Technical 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.

Official references

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