CVE-2026-66393

highCVSS 7.5covered by 1 sourcefirst seen 2026-08-22

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.

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Exploitation outlook

Low exploitation risk0.49% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 40% of all EPSS-scored CVEs.

Advisory coverage (1)

highCVE-2026-66393: NLTK versions before 3.9.4 contain an unbounded recursion vulnerability in JSONTaggedDecoder.d…nvd · 2026-08-22

External references

NVD record for CVE-2026-66393

CVE.org record

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