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Vulnerability record · CVE-2026-86430 · published 7 September 2026

CVE-2026-86430: Thephpleague commonmark vulnerability

Thephpleague · Commonmark

league/commonmark versions before 2.9.1 contain multiple denial of service vulnerabilities in fenced code block detection, reference link label lookup, and emphasis delimiter processing that perform super-linear work on crafted input. Attackers can submit specially crafted Markdown with long backtick runs, nested brackets, or delimiter sequences to consume disproportionate CPU time and prevent legitimate requests from completing.

8.7 CVSS 4.0 High EPSS 0.49% · top 60.1% CWE-407 · CWE-407
8.7CVSS 4.0 base score
0.49%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
10 Sep 2026Last modified by NVD

Description

league/commonmark versions before 2.9.1 contain multiple denial of service vulnerabilities in fenced code block detection, reference link label lookup, and emphasis delimiter processing that perform super-linear work on crafted input. Attackers can submit specially crafted Markdown with long backtick runs, nested brackets, or delimiter sequences to consume disproportionate CPU time and prevent legitimate requests from completing.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/thephpleague/commonmark/security/advisories/GHSA-j8pm-gj4c-rq4x MitigationVendor AdvisoryPatch
https://www.vulncheck.com/advisories/league-commonmark-before-2.9.1-denial-of-service-via-parsing Third Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

8.7CVE-2026-86428Thephpleague commonmark vulnerabilitycommonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named at…EPSS 0.49%8.7CVE-2026-86429Thephpleague commonmark vulnerabilityThe league/commonmark (thephpleague/commonmark) library in versions >= 1.5.0 and < 2.9.1 contains quadratic parsing complexity in its SmartPunctExten…EPSS 0.52%6.9CVE-2026-86431Thephpleague commonmark cross-site scripting vulnerabilityleague/commonmark (thephpleague/commonmark) versions >= 2.7.0 and < 2.9.1 contain a cross-site scripting vulnerability in the AttributesExtension. Pr…EPSS 0.39%6.3CVE-2026-33347Thephpleague commonmark cross-site scripting vulnerabilityleague/commonmark is a PHP Markdown parser. From version 2.3.0 to before version 2.8.2, the DomainFilteringAdapter in the Embed extension is vulnerab…EPSS 0.32%6.1CVE-2019-10010Thephpleague commonmark cross-site scripting vulnerabilityCross-site scripting (XSS) vulnerability in the PHP League CommonMark library before 0.18.3 allows remote attackers to insert unsafe links into HTML …EPSS 1.1%6.1CVE-2018-20583Thephpleague commonmark cross-site scripting vulnerabilityCross-site scripting (XSS) vulnerability in the PHP League CommonMark library versions 0.15.6 through 0.18.x before 0.18.1 allows remote attackers to…EPSS 1.6%5.1CVE-2026-30838Thephpleague commonmark cross-site scripting vulnerabilityleague/commonmark is a PHP Markdown parser. Prior to version 2.8.1, the DisallowedRawHtml extension can be bypassed by inserting a newline, tab, or o…EPSS 0.24%

Source: NIST National Vulnerability Database (record CVE-2026-86430), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.