CVE-2026-78683
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.
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Exploitation outlook
- Low exploitation risk0.28% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 19% of all EPSS-scored CVEs.
Advisory coverage (1)
External references
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