CVE-2026-78683: NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization vulnerability in the Transition
Summary
NLTK (Natural Language Toolkit, a Python library for processing human language) versions 3.9.4 and earlier have a vulnerability in their TransitionParser.parse() method that allows attackers to run arbitrary code by providing a malicious model file. The problem occurs because the code uses unsafe deserialization (pickle_load, a method that converts saved Python objects back into code) without proper restrictions, so it will execute hidden malicious commands embedded in a crafted model file when the application loads it.
Solution / Mitigation
Update NLTK to version 3.10.0 or later, which fixes this vulnerability.
Vulnerability Details
9.6(critical)
EPSS: 0.0%
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
network
low
none
required
August 24, 2026
Classification
Taxonomy References
Affected Vendors
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Original source: https://nvd.nist.gov/vuln/detail/CVE-2026-78683
First tracked: August 25, 2026 at 02:08 AM
Classified by LLM (prompt v3) · confidence: 92%