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    CVE-2021-42717

    ModSecurity 3.x through 3.0.5 mishandles excessively nested JSON objects. Crafted JSON objects with nesting tens-of-thousands deep could result in the web server being unable to service legitimate requests. Even a moderately large (e.g., 300KB) HTTP request can occupy one of the limited NGINX worker processes for minutes and consume almost all of the available CPU on the machine. Modsecurity 2 is similarly vulnerable: the affected versions include 2.8.0 through 2.9.4.

    Published:Dec 7, 2021
    Last Modified:Jul 3, 2025
    EPS:Dec 7, 2021
    EPSS Score:0.02217
    CVSS Score:7.5

    Affected Products

    Vendor
    Debian
    Product
    Debian Linux
    Vendor
    F5
    Product
    Nginx Modsecurity Waf
    Vendor
    Oracle
    Product
    Http Server
    Vendor
    Oracle
    Product
    Zfs Storage Appliance Kit
    Vendor
    Owasp
    Product
    Modsecurity
    Vendor
    Trustwave
    Product
    Modsecurity

    Exploits

    https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717/https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modsecurity-dos-vulnerability-in-json-parsing-cve-2021-42717/https://github.com/EkamSinghWalia/Detection-and-Mitigation-script-for-CVE-2021-42717

    Common Weakness Enumeration

    CWE-674 Uncontrolled Recursion

    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