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    CVE-2026-73321

    XenForo before 2.3.13 contains an uncontrolled recursion vulnerability in the BBCode parser that allows authenticated attackers to cause persistent denial of service by submitting a post with deeply nested BBCode tags. Attackers can craft a single malicious post with sufficient nesting depth to exceed PHP's stack limit, causing fatal errors that repeatedly terminate PHP-FPM workers for all visitors rendering the affected thread.

    Published:Sep 8, 2026
    Last Modified:Sep 9, 2026
    EPS:Sep 8, 2026
    EPSS Score:
    CVSS Score:6.5

    Affected Products

    Vendor
    Xenforo
    Product
    Xenforo

    Exploits

    https://github.com/BomboBombone/CVE-2026-73321

    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