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.
Fix
Patch, vendor advisory and mitigation references on NVD 2
- https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw Exploit, Mitigation, Vendor Advisory
- https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw Exploit, Mitigation, Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 8.7 · nltkNVD modified 2026-10-14 13:10
Affected (CPE criteria) 1
cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*
References 3
- https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw Exploit, Mitigation, Vendor Advisory
- https://www.vulncheck.com/advisories/nltk-before-denial-of-service-via-jsontaggeddecoder Third Party Advisory
- https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw Exploit, Mitigation, Vendor Advisory