High [CVE-2026-66393] Denial of Service via unbounded recursion in JSONTaggedDecoder
This high-severity Red Hat Linux advisory covers CVE-2026-66393 affecting Red Hat Ansible Automation Platform 2.
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Summary
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.
A flaw was found in NLTK. This can cause the Python process to crash, leading to a denial of service.
A denial of service flaw exists in NLTK's JSONTaggedDecoder, allowing remote attackers to crash Python processes by submitting crafted, deeply nested JSON data.
This vulnerability poses a significant risk to Red Hat products that process untrusted JSON input using affected NLTK versions, as it can lead to service unavailability without requiring authentication or user interaction. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
Weakness: CWE-606. Affected Red Hat products: Red Hat Ansible Automation Platform 2.
Red Hat lists Exploit Intelligence; Lightspeed Core; OpenShift Lightspeed; Red Hat OpenShift AI (RHOAI) as not affected. Red Hat does not currently list a fixing RHSA for this CVE.
- < 3.9.4
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Mitigation checklist
- To mitigate this vulnerability, implement input validation to restrict the maximum nesting depth of JSON structures processed by NLTK. Ensure that any services or applications utilizing NLTK's JSONTaggedDecoder do not process untrusted or excessively nested JSON input without prior sanitization. If NLTK is not required to process external JSON, restrict its exposure to such data.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
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