league/commonmark: Denial of service via duplicate footnote definitions

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 The Footnote extension records one backref per footnote reference and then appends the entire backref list for every footnote definition block in the document, without ever de-duplicating or removing repeated definitions of the same label (GatherFootnotesListener, populated by NumberFootnotesListener). A document that references a single label N times and also supplies N duplicate [^a]: definitions of that label therefore produces N × N FootnoteBackref nodes, so output size, parse time, and peak memory are all O(N²). Reaching the vulnerable path requires FootnoteExtension to be registered on the Environment. This is opt-in, but is a commonly enabled GFM-style feature; no other non-default configuration is required. An unauthenticated attacker can expand a ~10 KB request into a ~62 MB HTML response, ~3 s of CPU, and ~440 MB of peak memory — enough to OOM-kill a default 128 MB PHP worker and deny service. Availability impact only; no confidentiality or integrity effect. The…

Published by the source

6 Aug 2026, 20:40 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-jfm3-95jq-q3rf

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-jfm3-95jq-q3rf

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# Patch Next advisory brief: GHSA-jfm3-95jq-q3rf

Advisory: league/commonmark: Denial of service via duplicate footnote definitions
IDs: GHSA-jfm3-95jq-q3rf
Record: https://patchnext.com/advisories/ghsa-jfm3-95jq-q3rf (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-jfm3-95jq-q3rf (OSV record GHSA-jfm3-95jq-q3rf lists affected ranges: Packagist league/commonmark >=1.5.0 <2.9.0 (fixed))
- Verified: https://github.com/advisories/GHSA-jfm3-95jq-q3rf (GitHub-reviewed advisory GHSA-jfm3-95jq-q3rf lists affected ranges: Packagist league/commonmark >=1.5.0 <2.9.0)

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