CVE-2026-66393

HIGH 7.5

NLTK before 3.9.4 Denial of Service via JSONTaggedDecoder

CVSS Score

7.5

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-674
Vendor	nltk
Product	nltk
Published	Aug 22, 2026

Stay Ahead of the Next One

Get instant alerts for nltk nltk

Be the first to know when new high vulnerabilities affecting nltk nltk are published — delivered to Slack, Telegram or Discord.

Get Free Alerts → Free · No credit card · 60 sec setup

CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Affected Versions

nltk / nltk

0 < 3.9.4

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw vulncheck.com: https://www.vulncheck.com/advisories/nltk-before-denial-of-service-via-jsontaggeddecoder

Credits

🔍 ZeroXJacks