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CVE-2026-66393 Details

Description

NLTK versions before 3.9.4 contain an unbounded recursion vulnerability in JSONTaggedDecoder.decode_obj() that allows attackers to cause denial of service by supplying deeply nested JSON structures. Attackers can craft JSON payloads exceeding the recursion limit to trigger an unhandled RecursionError that crashes the Python process.

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:7.5 HIGHVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw	CISA-ADP	ExploitMitigationVendor Advisory
https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw	[email protected]	ExploitMitigationVendor Advisory
https://www.vulncheck.com/advisories/nltk-before-denial-of-service-via-jsontaggeddecoder	[email protected]	Third Party Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-674	Uncontrolled Recursion	[email protected]

Affected Products

Product	Versions
nltk nltk	< 3.9.4
CPE cpe:2.3:a:nltk:nltk:::::::: Remediation No remediation found in references.

Change History

4 change records found show changes

Date	Action	Recorded By
Aug 27, 2026	Initial Analysis	[email protected]
Aug 26, 2026	CVE Modified	[email protected]
Aug 26, 2026	CVE Modified	CISA-ADP
Aug 22, 2026	New CVE Received	[email protected]