HighCVE-2026-71488

    league/commonmark: Quadratic-time denial of service when parsing crafted Markdown (CVE-2026-71488)

    Published Last modified Sources: CVE.org, EUVD, OSV

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    What is affected, what to do

    league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 0.6.0 until 2.9.0, specially crafted Markdown lines can cause the parser to have quadratic time complexity when converting, because several parsing paths repeatedly rescan growing portions of a line to translate between character positions and byte positions, and the Autolink extension can also copy and validate the remaining line at every URL-like prefix, allowing an attacker who can submit Markdown for conversion to consume disproportionate CPU time with a comparatively small request.

    The available sources name no fixed version. Check the vendor guidance in the references below.

    Affected
    • thephpleague (The League of Extraordinary Packages) CommonMark gte 0.6.0, < 2.9.0..*

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.5

    XIEM Effective CVSS

    Highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org, EUVD, OSV

    0.6 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 50.7

    Show all metrics
    Severity
    High
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    79.41 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.5 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.6 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    50.7
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 7 August 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-407, CWE-1050

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 0.6.0 until 2.9.0, specially crafted Markdown lines can cause the parser to have quadratic time complexity when converting, because several parsing paths repeatedly rescan growing portions of a line to translate between character positions and byte positions, and the Autolink extension can also copy and validate the remaining line at every URL-like prefix, allowing an attacker who can submit Markdown for conversion to consume disproportionate CPU time with a comparatively small request. This issue is fixed in 2.9.0.

    Source: NVD (NIST), CVE.org (MITRE), cvelistv5, ENISA EUVD, OSV (Open Source Vulnerabilities)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    thephpleaguecommonmark
    • ≥ 0.6.0, < 2.9.0
    • —
    packagistleague/commonmark
    • 1.0.0-beta2
    • 1.6.7
    • 0.19.2
    • 1.3.2
    • 0.15.1
    • 0.15.2
    • 0.9.0
    • 2.3.6
    • 0.7.2
    • 0.19.0
    • 2.8.1
    • 0.17.0
    • 1.5.1
    • 0.13.2
    • 0.11.2
    • 2.6.2
    • 2.3.9
    • 2.0.0-beta2
    • 1.5.3
    • 1.6.4
    • 1.6.1
    • 1.1.3
    • 2.3.5
    • 1.0.0-beta3
    • 0.18.4
    • 0.17.3
    • 0.8.0
    • 0.13.0
    • 1.5.5
    • 1.5.4
    • 1.0.0-rc1
    • 1.4.3
    • 0.15.5
    • 0.7.1
    • 1.6.3
    • 1.1.0
    • 2.1.3
    • 1.5.6
    • 0.12.0
    • 2.0.0-beta3
    • 0.15.7
    • 2.2.0
    • 2.4.4
    • 2.0.0-beta1
    • 2.5.0
    • 1.5.7
    • 2.3.8
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    Vendors and products

    Weakness classes (CWE)

    • CWE-407Inefficient Algorithmic Complexity

      Class

      An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.

      Entry at MITRE CWE-407

    • CWE-1050Excessive Platform Resource Consumption within a Loop

      Base

      The product has a loop body or loop condition that contains a control element that directly or indirectly consumes platform resources, e.g. messaging, sessions, locks, or file descriptors.

      Entry at MITRE CWE-1050

    References & sources

    • github.comthephpleague/commonmark/security/advisories/GHSA-2q4p-g7hv-5rgvweb, x_refsource_CONFIRM, euvd
    • github.comthephpleague/commonmark/commit/a6ef6cdc308dfa39a34239c35818e758…web, x_refsource_MISC, euvd
    • github.comthephpleague/commonmark/commit/a70979ea0d7d3377bd7127536748454a…web, x_refsource_MISC, euvd
    • github.comthephpleague/commonmark/commit/c97b02e5e652b992033b93ba5d6182f7…web, x_refsource_MISC, euvd
    • github.comthephpleague/commonmarkpackage
    • github.comthephpleague/commonmark/releases/tag/2.9.0web, x_refsource_MISC, euvd

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: yes

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-71488","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-08-07T17:16:54.394661Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. ReceivedGitHub

      CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

      Weakness type: CWE-407, CWE-1050

      Description added or changed

      Show 10 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      commonmark
      Descriptionadded
      —
      league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 0.6.0 until 2.9.0, specially crafted Markdown lines can cause the parser to have quadratic time complexity when converting, because several parsing paths repeatedly rescan growing portions of a line to translate between character positions and byte positions, and the Autolink extension can also copy and validate the remaining line at every URL-like prefix, allowing an attacker who can submit Markdown for conversion to consume disproportionate CPU time with a comparatively small request. This issue is fixed in 2.9.0.
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
      Weakness type (CWE)added
      —
      CWE-407
      Weakness type (CWE)added
      —
      CWE-1050
      Referenceadded
      —
      https://github.com/thephpleague/commonmark/commit/a6ef6cdc308dfa39a34239c35818e75892a0e6a8
      Referenceadded
      —
      https://github.com/thephpleague/commonmark/commit/a70979ea0d7d3377bd7127536748454a922bf5eb
      Referenceadded
      —
      https://github.com/thephpleague/commonmark/commit/c97b02e5e652b992033b93ba5d6182f706343fc6
      Referenceadded
      —
      https://github.com/thephpleague/commonmark/releases/tag/2.9.0
      Referenceadded
      —
      https://github.com/thephpleague/commonmark/security/advisories/GHSA-2q4p-g7hv-5rgv

      Source identifier: security-advisories@github.com

    2 NVD translations into other languages are hidden.

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