UBUNTU-CVE-2026-121438

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    UBUNTU-CVE-2026-121438

    Published: 3 Nov 2026Last Modified: 5 Nov 2026
    Upstream:
    CVE-2026-121438

    Summary:

    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://ubuntu.com/security/CVE-2026-121438, https://www.cve.org/CVERecord?id=CVE-2026-121438, https://github.com/lepture/mistune/security/advisories/GHSA-47p6-w2rc-5qf7, https://github.com/lepture/mistune/commit/fe02f40faf091f86da9ed62c865f31e11da111d7, https://github.com/lepture/mistune/commit/fe02f40faf091f86da9ed62c865f31e11da111d7, https://www.vulncheck.com/advisories/mistune-before-3.3.3-denial-of-service-via-balanced-bracket-link-parsing

    Affected packages

    Package

    Name: mistune

    Purl: pkg:deb/ubuntu/mistune?arch=source&distro=xenial

    Affected ranges

    Type: ECOSYSTEM

    Events:

    Introduced- 0
    Fixed -None

    Affected versions

    0.6-2

    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
    UBUNTU-CVE-2026-121438 | CVE-DB