CVE-2026-66393

EUVD-2026-64310
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.
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
VulnCheckCNA
7.5 HIGH
NETWORK
LOW
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Base Score
CVSS 3.x
EPSS Score
Percentile: Unknown
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources.
VendorProductVersionSource
nltknltk
𝑥
< 3.9.4
CNA
Debian logo
Debian Releases
Debian Product
Codename
nltk
bookworm
vulnerable
bullseye
vulnerable
forky
3.10.3-1
fixed
sid
3.10.3-1
fixed
trixie
vulnerable
Common Weakness Enumeration
References
https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw
https://www.vulncheck.com/advisories/nltk-before-denial-of-service-via-jsontaggeddecoder