Bug 2521342 (CVE-2026-66393)

Summary: CVE-2026-66393 nltk: NLTK: Denial of Service via unbounded recursion in JSONTaggedDecoder
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: anpicker, bparees, dschmidt, ebourniv, hasun, jfula, jlanda, jowilson, kshier, nyancey, ometelka, ptisnovs, sbunciak, simaishi, stcannon, syedriko, teagle, xdharmai, yguenane
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in NLTK. A remote attacker can exploit an unbounded recursion vulnerability in the JSONTaggedDecoder.decode_obj() function by supplying deeply nested JSON structures. This can cause the Python process to crash, leading to a denial of service.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-08-22 14:32:17 UTC
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.