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Vulnerability record · CVE-2026-86428 · published 7 September 2026

CVE-2026-86428: Thephpleague commonmark vulnerability

Thephpleague · Commonmark

commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named attributes. Attackers can submit Markdown with numerous distinct attribute names to cause quadratic-time attribute merging and filtering, consuming disproportionate CPU resources and preventing 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
9 Sep 2026Last modified by NVD

Description

commonmark versions from 1.5.0 before 2.10.0 contain a denial of service vulnerability in the AttributesExtension when processing distinctly-named attributes. Attackers can submit Markdown with numerous distinct attribute names to cause quadratic-time attribute merging and filtering, consuming disproportionate CPU resources and preventing 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-8rr7-cvq3-gmfh MitigationVendor Advisory
https://www.vulncheck.com/advisories/commonmark-1.5.0-before-2.10.0-denial-of-service-via-attributes Third Party Advisory

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Related vulnerabilities

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

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%8.7CVE-2026-86430Thephpleague commonmark vulnerabilityleague/commonmark versions before 2.9.1 contain multiple denial of service vulnerabilities in fenced code block detection, reference link label looku…EPSS 0.49%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-2026-86428), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.