{"id":"GHSA-g2gp-3wwq-f4ph","aliases":[],"title":"league/commonmark: Denial of service via adjacent inline attribute blocks","titleSource":"OSV","descriptionSource":"OSV","declaredSeverity":"HIGH","description":"### Impact\n\nWith 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)**.\n\nReaching 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 `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 — 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** — 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.","severity":"high","score":7.5,"published":"2026-08-06T20:39:52.000Z","modified":"2026-08-06T20:45:15.558Z","withdrawn":false,"knownExploited":false,"affected":[{"ecosystem":"Packagist","name":"league/commonmark","sources":[{"name":"OSV · GHSA-g2gp-3wwq-f4ph","url":"https://osv.dev/vulnerability/GHSA-g2gp-3wwq-f4ph"}],"ranges":[{"events":[{"introduced":"1.5.0"},{"fixed":"2.9.0"}],"type":"ECOSYSTEM"}],"versions":["1.5.0","1.5.1","1.5.2","1.5.3","1.5.4","1.5.5","1.5.6","1.5.7","1.5.8","1.6.0","1.6.1","1.6.2","1.6.3","1.6.4","1.6.5","1.6.6","1.6.7","2.0.0","2.0.0-beta1","2.0.0-beta2","2.0.0-beta3","2.0.0-rc1","2.0.0-rc2","2.0.1","2.0.2","2.0.3","2.0.4","2.1.0","2.1.1","2.1.2","2.1.3","2.2.0","2.2.1","2.2.2","2.2.3","2.2.4","2.2.5","2.3.0","2.3.1","2.3.2","2.3.3","2.3.4","2.3.5","2.3.6","2.3.7","2.3.8","2.3.9","2.4.0","2.4.1","2.4.2","2.4.3","2.4.4","2.5.0","2.5.1","2.5.2","2.5.3","2.6.0","2.6.1","2.6.2","2.7.0","2.7.1","2.8.0","2.8.1","2.8.2","2.8.3"],"fixed":["2.9.0"]}],"sourceAffected":[],"references":["https://github.com/thephpleague/commonmark/security/advisories/GHSA-g2gp-3wwq-f4ph","https://github.com/thephpleague/commonmark/commit/2d4c0fafa62501be919262064cffa6d71687430b","https://github.com/thephpleague/commonmark","https://github.com/thephpleague/commonmark/releases/tag/2.9.0"],"sources":[{"name":"OSV","id":"GHSA-g2gp-3wwq-f4ph","modified":"2026-08-06T20:45:15.558862305Z","url":"https://osv.dev/vulnerability/GHSA-g2gp-3wwq-f4ph"}],"assessments":[{"source":"OSV","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5}],"products":[],"remediation":[],"kev":{"status":"unavailable","checkedAt":"2026-10-28T19:25:35.956Z"},"coverage":[{"source":"NVD","status":"not-checked"},{"source":"GHSA","status":"not-checked"},{"source":"EUVD","status":"not-checked"},{"source":"EPSS","status":"not-checked"}],"evidence":[]}