What is CVE-2026-66393?

CVE-2026-66393 is a high-severity vulnerability in Nltk, classified under Uncontrolled Recursion. CVSS score: 7.5/10. Published 2026-08-22.

How severe is CVE-2026-66393?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Nltk

CVE-2026-66393

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.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

Nltk

Weakness classification (CWE)

CWE-674 — Uncontrolled Recursion

References

disclosure@vulncheck.com (vendor-advisory)
disclosure@vulncheck.com (third-party-advisory)

Frequently asked questions

What is CVE-2026-66393?: CVE-2026-66393 is a high-severity vulnerability in Nltk, classified under Uncontrolled Recursion. CVSS score: 7.5/10. Published 2026-08-22.
How severe is CVE-2026-66393?: High severity. CVSS v3 base score is 7.5 out of 10.