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
NISTPrimary
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: 42.32%
Affected Products (NVD)
VendorProductVersion
nltknltk
𝑥
< 3.9.4
𝑥
= Vulnerable software versions
Debian logo
Debian Releases
Debian Product
Codename
nltk
bookworm
postponed
forky
3.10.3-1
fixed
sid
3.10.3-1
fixed
trixie
no-dsa
Ubuntu logo
Ubuntu Releases
Ubuntu Product
Codename
nltk
bionic
needs-triage
focal
needs-triage
jammy
needs-triage
noble
needs-triage
resolute
needs-triage
trusty
needs-triage
xenial
needs-triage
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
https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw