CVE-2026-121438

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    CVE-2026-121438

    Published: 3 Nov 2026Last Modified: 5 Nov 2026

    Summary: Mistune before 3.3.3 Denial of Service via Balanced Bracket Link Parsing

    Details: 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.

    References: https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/121xxx/CVE-2026-121438.json, https://github.com/lepture/mistune/security/advisories/GHSA-47p6-w2rc-5qf7, https://nvd.nist.gov/vuln/detail/CVE-2026-121438, https://www.vulncheck.com/advisories/mistune-before-3.3.3-denial-of-service-via-balanced-bracket-link-parsing, https://github.com/lepture/mistune/commit/fe02f40faf091f86da9ed62c865f31e11da111d7

    Affected packages

    Package

    Name:

    Purl:

    Affected ranges

    Type: GIT

    Events:

    Introduced- 0
    Fixed -060f73ac87e8cf6d9e9b48f2df28c0654d845a4c

    Affected versions

    v3.3.2
    v3.3.1
    v3.3.0

    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
    CVE-2026-121438 | CVE-DB