CVE-2026-78683
NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization
- State
- Published
- Severity
- 9.4 Critical
- Published
- Aug 25, 2026
- Updated
- Aug 25, 2026
- Reserved
- Aug 25, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 9.4 Critical | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H | VulnCheck |
| 3.1 | 9.6 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H | VulnCheck |
Weaknesses
- CWE-502 Deserialization of Untrusted Data
Affected Products
| Product | Versions |
|---|---|
nltknltk |
|
References
- GitHub Security Advisory (GHSA-rhp5-r9x4-f5g2)vendor-advisory
- VulnCheck Advisory: NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserializationthird-party-advisory
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