7.5highHigh
CVE-2026-66393
Nltk Nltk
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.
Exploitation status
- Published references include exploit or proof-of-concept material. There is no confirmation it is being used in real attacks.
- A vendor advisory or patch reference has been published.
What the metrics mean
- It is reachable over a network, without needing local access.
- For an attacker who can reach it, no special conditions are needed to exploit it.
- To exploit it, no account is needed.
- Beyond that, no action by a user is required.
Scoring
- CVSS
- 7.5 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- CVSS v4
- 8.7
- Weakness
- CWE-674
- Assigned by
- disclosure@vulncheck.com
Dates
- Published
- 2026-08-22
- Last modified
- 2026-08-27
- Sources
- NVD
Affected products
- Nltk Nltk- 3.9.4
As listed in the NVD configuration data. Not a statement about your estate.