{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "league/commonmark"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.5.0"
            },
            {
              "fixed": "2.9.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-407"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-06T20:39:52Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Impact\n\nWith the Attributes extension enabled, `AttributesListener::findTargetAndDirection()` resolves each attribute node\u0027s 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 \u0398(N) and the whole run is **\u0398(N\u00b2)**.\n\nReaching the path requires `AttributesExtension` (opt-in, but first-party: `League\\CommonMark\\Extension\\Attributes\\AttributesExtension`). No other configuration matters \u2014 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 `allow_unsafe_links`. 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 \u2014 a cheap denial of service. Availability impact only. **The Attributes extension was introduced in 1.5.0 (May 2020) with this outward-walk resolver present from the first commit, so all releases from 1.5.0 onward (including every 2.x) are affected.**\n\n### Workarounds\n\nThere is no library-level configuration that gates the quadratic walk. Integrators who cannot upgrade can only reduce exposure indirectly:\n\n- **Disable the Attributes extension** for untrusted input, or\n- **Impose a strict maximum input length before conversion** \u2014 noting that because the cost is quadratic, even a modest cap must be small to meaningfully bound worst-case CPU.\n\nUpgrading to a release containing the fix is recommended.",
  "id": "GHSA-g2gp-3wwq-f4ph",
  "modified": "2026-08-06T20:39:52Z",
  "published": "2026-08-06T20:39:52Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/thephpleague/commonmark/security/advisories/GHSA-g2gp-3wwq-f4ph"
    },
    {
      "type": "WEB",
      "url": "https://github.com/thephpleague/commonmark/commit/2d4c0fafa62501be919262064cffa6d71687430b"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/thephpleague/commonmark"
    },
    {
      "type": "WEB",
      "url": "https://github.com/thephpleague/commonmark/releases/tag/2.9.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "league/commonmark: Denial of service via adjacent inline attribute blocks"
}