league/commonmark: Denial of service in the SmartPunct and Attributes extensions

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-2026-86429: 0.52% estimated exploitation activity in the next 30 days; percentile 43.94 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Two first-party extensions contain quadratic parsing paths. Both ship with the library but must be explicitly registered on the Environment; neither is included in CommonMarkConverter, GithubFlavoredMarkdownConverter, or GithubFlavoredMarkdownExtension. Applications that do not register SmartPunctExtension or AttributesExtension are not affected by this advisory. 1. SmartPunctExtension — quote replacement recopies the whole text node (affected from 2.0.0). ReplaceUnpairedQuotesListener converts each unpaired Quote node back to a Text node and merges it into its neighbours via AdjacentTextMerger. The merge reads the left node's literal into a local variable, appends to that variable, and writes it back — and because the read aliases the node's string, every append copies the entire accumulated literal rather than only the bytes added. The listener runs this once per surviving unpaired quote against the same continuously growing text node, so the same buffer is fully re-copied a…

Published by the source

1 Sep 2026, 20:21 UTC

Last modified by the source

8 Sep 2026, 12:38 UTC

Source last checked

26 Oct 2026, 14:51 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jjv6-8j6v-6j52

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-jjv6-8j6v-6j52

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# Patch Next advisory brief: CVE-2026-86429

Advisory: league/commonmark: Denial of service in the SmartPunct and Attributes extensions
IDs: CVE-2026-86429, GHSA-jjv6-8j6v-6j52
Record: https://patchnext.com/advisories/cve-2026-86429 (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 2.9.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist league/commonmark: affected >= 1.5.0, < 2.9.1; fixed in 2.9.1

## 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-jjv6-8j6v-6j52 (OSV record GHSA-jjv6-8j6v-6j52 lists affected ranges: Packagist league/commonmark >=1.5.0 <2.9.1 (fixed))
- Verified: https://github.com/advisories/GHSA-jjv6-8j6v-6j52 (GitHub-reviewed advisory GHSA-jjv6-8j6v-6j52 lists affected ranges: Packagist league/commonmark >=1.5.0 <2.9.1)

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