UBUNTU-CVE-2026-121437

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    UBUNTU-CVE-2026-121437

    Published: 3 Nov 2026Last Modified: 5 Nov 2026
    Upstream:
    CVE-2026-121437

    Summary:

    Details: Mistune from 3.3.0 before 3.3.4 contains a denial of service vulnerability that allows remote attackers to exhaust CPU through quadratic-time emphasis delimiter processing. Attackers can submit small markdown documents with repeated patterns like "*a_b" to trigger an O(n²) index-fixup loop, stalling workers for seconds.

    References: https://ubuntu.com/security/CVE-2026-121437, https://www.cve.org/CVERecord?id=CVE-2026-121437, https://github.com/lepture/mistune/security/advisories/GHSA-qp42-r9j6-83g9, https://github.com/lepture/mistune/commit/b4dd3284e52ec741ed9a227db29ade9017828e90, https://github.com/lepture/mistune/commit/b4dd3284e52ec741ed9a227db29ade9017828e90, https://www.vulncheck.com/advisories/mistune-3.3.0-before-3.3.4-quadratic-time-dos-via-process-emphasis-delimiters

    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-2026-121437 | CVE-DB