CriticalVulnerability

CVE-2026-78683: NLTK unsafe pickle deserialization in TransitionParser.parse() method

Source: NVD(opens in a new tab)
Identifier: CVE-2026-78683
Published: August 24, 2026
Record updated: October 9, 2026

Affected: nltk <= 3.9.4
Fixed in: 3.10.0
released July 7, 2026, 48 days before disclosure
Known exploitation: Not listed in the CISA Known Exploited Vulnerabilities catalog at the last check.
EPSS: 0.5%

Summary

NLTK before 3.10.0 (affected versions <=3.9.4) has an unsafe pickle deserialization flaw in TransitionParser.parse() (nltk/parse/transitionparser.py). The method calls pickle_load() with restricted=False, routing loads through WarningUnpickler, which does not override find_class(), so arbitrary class resolution is allowed. 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.

Mitigation

Fixed in 3.10.0.

Details

Scores and exploitation

CVSS score: 9.6(critical)
Patch available: Yes
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Attack vector: network
Attack complexity: low
Privileges required: none
User interaction: required
EPSS: 0.5%Estimated probability that this CVE is exploited in the next 30 days, from the FIRST Exploit Prediction Scoring System. Read on November 4, 2026.
Disclosure date: August 24, 2026

Weaknesses and techniques

Weakness (CWE): CWE-502
Attack pattern (CAPEC): CAPEC-586
AI threat technique (MITRE ATLAS): AML.T0010

Affected

Packages: nltk@<= 3.9.4 (fixed: 3.10.0)

Classification

Attack type: Supply chain
Attack sophistication: Trivial
AI component targeted: Framework
Impact: Confidentiality,
Integrity,
Availability
Labels: security

How this record was produced

Summaries, mitigations and labels on this page are generated automatically from the source. The linked source is authoritative. The source gives this advisory a description and no title, so the title above is a headline generated from the source text.

Original source: https://nvd.nist.gov/vuln/detail/CVE-2026-78683

First tracked: August 25, 2026 at 02:08 AM ET, from NVD/CVE Database

Classifier: claude-haiku-5-5, prompt v4

Classifier confidence: 85% (self-assessed)

Affected packages in the Exposure Registry

Matched by package name and ecosystem. Each entry shows whether the package delegates to a language model and how many tracked packages depend on it.

nltkPyPINo LLM dependency detected · 47 tracked dependents

Topics

Model and package supply chain

Summary

Mitigation

Affected packages in the Exposure Registry

Topics

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