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    CVE-2026-121438

    Mistune before 3.3.3 contains a denial of service vulnerability in InlineParser.parse_link that allows attackers to cause quadratic CPU growth by supplying balanced nested brackets. Attackers can submit crafted Markdown with thousands of nested bracket pairs not forming a valid link, triggering repeated _contains_nested_link scans that exhaust CPU in parsing applications.

    Published:Nov 3, 2026
    Last Modified:Nov 4, 2026
    EPS:Nov 3, 2026
    EPSS Score:
    CVSS Score:5.3

    Affected Products

    Vendor
    Lepture
    Product
    Mistune
    Vendor
    Mistune Project
    Product
    Mistune

    Exploits

    No exploit reference

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    CVE-2026-59925 (CVSS 7.5) — Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, long sequences of well-formed …
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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