league/commonmark: Denial of service via adjacent inline attribute blocks

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

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Impact With the Attributes extension enabled, AttributesListener::findTargetAndDirection() resolves each attribute node's target by walking outward through its siblings. For a run of N adjacent inline attribute blocks placed at the start of a block (with nothing to their left), each node scans the entire sibling list to the far-right end before giving up and falling back to the parent. Each resolution is therefore Θ(N) and the whole run is Θ(N²). Reaching the path requires AttributesExtension (opt-in, but first-party: League\CommonMark\Extension\Attributes\AttributesExtension). No other configuration matters — the quadratic walk runs unconditionally during parsing and is not gated by the attributes/allow allow-list, the on hardening added in 2.7.0, or allowunsafelinks. An unauthenticated attacker can submit a ~32 KB input ({#a} repeated 8,000 times) that takes over 5 seconds to convert, with time growing quadratically in input length — a cheap denial of service. Availability impact…

Published by the source

6 Aug 2026, 20:39 UTC

Last modified by the source

6 Aug 2026, 20:45 UTC

Source last checked

26 Oct 2026, 14:50 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-g2gp-3wwq-f4ph

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-g2gp-3wwq-f4ph

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# Patch Next advisory brief: GHSA-g2gp-3wwq-f4ph

Advisory: league/commonmark: Denial of service via adjacent inline attribute blocks
IDs: GHSA-g2gp-3wwq-f4ph
Record: https://patchnext.com/advisories/ghsa-g2gp-3wwq-f4ph (revision 2, source checked 26 Oct 2026, 14:50 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 2.9.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist league/commonmark: affected >= 1.5.0, < 2.9.0; fixed in 2.9.0

## 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-g2gp-3wwq-f4ph (OSV record GHSA-g2gp-3wwq-f4ph lists affected ranges: Packagist league/commonmark >=1.5.0 <2.9.0 (fixed))
- Verified: https://github.com/advisories/GHSA-g2gp-3wwq-f4ph (GitHub-reviewed advisory GHSA-g2gp-3wwq-f4ph lists affected ranges: Packagist league/commonmark >=1.5.0 <2.9.0)

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