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PYSEC-2026-3724

Quick fix

PYSEC-2026-3724 — nltk: upgrade to the fixed version with the command below.

pip install --upgrade 'nltk>=3.9.4'

Details

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.

Are you affected?

Enter the version of the package you're using.

Affected packages

PyPI/nltk

Introduced in: 0Fixed in: 3.9.4

Fixpip install --upgrade 'nltk>=3.9.4'

References

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