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…

Code

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No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

1. Aug 22, 2026 · NIST NVD

   Detected

   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.

2. Oct 14, 2026 · NIST NVD

   Updated

   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.

Affected

• cpe nltk/nltkversion unspecified

Sources

• CVE.orgVulnerability recordCVE-2026-66393

  Official CVE identifier

  cve.org
• FIRST EPSSExploitation probabilityCVE-2026-66393

  30-day exploitation probability 0.5%

  first.org
• NIST NVDVulnerability recordCVE-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 unh

  nvd.nist.gov

References

• Exploit · github.com
• Third Party Advisory · vulncheck.com