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High, CVSS 7.5amended

league/commonmark: Denial of service via distinctly-named attributes in the Attributes extension

CVE-2026-86428GHSA-8rr7-cvq3-gmfh

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (league/commonmark 2.10.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-86428: 0.49% estimated exploitation activity in the next 30 days; percentile 42.42 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact AttributesExtension ships with the library but must be explicitly registered on the Environment; it is not included in CommonMarkConverter, GithubFlavoredMarkdownConverter, or GithubFlavoredMarkdownExtension. Applications that do not register AttributesExtension are not affected by this advisory. Two paths in the extension re-process every attribute a node has already collected each time another attribute is applied to it. When the attributes carry distinct names, the collected set grows by one on every step and is walked again in full, so a run of n attributes costs O(n²). 1. Attribute nodes resolving to a common target (affected from 1.5.0). AttributesListener::processDocument() merges each attribute node into the set accumulated for its target, then filters the result. Both operations traverse that entire set: AttributesHelper::mergeAttributes() rebuilds it with arraymerge(), and AttributesHelper::filterAttributes() matches a regular expression against every name in it. A…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-8rr7-cvq3-gmfh

  2. Revision 1 · created ·

    Published from osv record GHSA-8rr7-cvq3-gmfh

Agent brief

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# Patch Next advisory brief: CVE-2026-86428

Advisory: league/commonmark: Denial of service via distinctly-named attributes in the Attributes extension
IDs: CVE-2026-86428, GHSA-8rr7-cvq3-gmfh
Record: https://patchnext.com/advisories/cve-2026-86428 (revision 2, source checked 26 Oct 2026, 14:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: league/commonmark 2.10.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist league/commonmark: affected >= 1.5.0, < 2.10.0; fixed in 2.10.0

## Suggested inspection (read-only)
- Packagist league/commonmark: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on league/commonmark.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-8rr7-cvq3-gmfh (OSV record GHSA-8rr7-cvq3-gmfh lists affected ranges: Packagist league/commonmark >=1.5.0 <2.10.0 (fixed))
- Verified: https://github.com/advisories/GHSA-8rr7-cvq3-gmfh (GitHub-reviewed advisory GHSA-8rr7-cvq3-gmfh lists affected ranges: Packagist league/commonmark >=1.5.0 <2.10.0)

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