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    CVE-2026-66393

    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.

    Published:Aug 22, 2026
    Last Modified:Aug 27, 2026
    EPS:Aug 22, 2026
    EPSS Score:0.00363
    CVSS Score:7.5

    Affected Products

    Vendor
    Nltk
    Product
    Nltk

    Exploits

    https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pwhttps://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw

    Common Attack Pattern Enumeration and Classification (CAPEC)

    CAPEC-230 Serialized Data with Nested Payloads
    CAPEC-231 Oversized Serialized Data Payloads

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    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High