Fluid Attacks Database

Description

NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed Python's recursion limit and raise an unhandled RecursionError, crashing applications that parse user-supplied feature structures or feature grammars.

Mitigation

Update Impact

Minimal update. May introduce new vulnerabilities or breaking changes.

Ecosystem	Component	Affected version	Patched versions
debian 12	nltk	=3.10.0-1 \|\| =3.10.1-1 \|\| =3.10.3-1 \|\| =3.8-1 \|\| =3.8.1-1 \|\| =3.9.1-1 \|\| =3.9.1-2 \|\| =3.9.2-1 \|\| =3.9.3-1	-
debian 13	nltk	=3.10.0-1 \|\| =3.10.1-1 \|\| =3.10.3-1 \|\| =3.9.1-2 \|\| =3.9.2-1 \|\| =3.9.3-1	-
debian 14	nltk	=3.10.0-1 \|\| =3.10.1-1 \|\| =3.9.1-2 \|\| =3.9.2-1 \|\| =3.9.3-1 \|\| >=0 <3.10.3-1	3.10.3-1
pypi	nltk	>=0 <3.10.3	3.10.3

Aliases

1. CVE-2026-817242. NVD-2026-817243. OSV-DEBIAN-2026-817244. OSV-2026-817245. GHSA-cw6x-m8jw-qmrh6. GCVE-2026-817247. SECURITY-TRACKER-CVE-2026-81724

References

1. https://github.com/nltk/nltk/security/advisories/GHSA-cw6x-m8jw-qmrh2. https://github.com/nltk/nltk/commit/43c7b78cc8ea37e5cd3a129e27e32c415ea21cf13. https://github.com/nltk/nltk/releases/tag/v3.10.34. https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3739.yaml5. https://www.vulncheck.com/advisories/nltk-before-3.10.3-denial-of-service-via-uncontrolled-recursion

Does your application use this vulnerable software?

During the free trial, our tools assess your application, identify vulnerabilities, and provide recommendations for their remediation.