GHSA-jfm3-95jq-q3rf
HIGHGHSA-jfm3-95jq-q3rf is a high-severity (CVSS 7.5) vulnerability in league/commonmark. O3 Security confirms whether GHSA-jfm3-95jq-q3rf is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
league/commonmark: Denial of service via duplicate footnote definitions
Blast Radius
league/commonmarkReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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 Footnote extension was introduced in 1.5.0 (May 2020) with this backref logic present from the first commit, so all releases from 1.5.0 onward (including every 2.x through 2.8.x) are affected.
Workarounds
There is no library-level option to cap the number of footnotes, references, or definitions, so no configuration switch prevents the amplification. Integrators who cannot upgrade should:
- Disable the Footnote extension for untrusted input, or
- Enforce a strict input-size limit before conversion — but note this is a weak control here, since the ~10 KB payload that already triggers the 62 MB / ~440 MB blowup is well within typical request-body limits, so any cap must be aggressively small to help.
Upgrading to the patched release is the recommended remediation.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | league/commonmark | ≥ 1.5.0&&< 2.9.0 | 2.9.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for league/commonmark. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update league/commonmark to 2.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-jfm3-95jq-q3rf is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-jfm3-95jq-q3rf is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-jfm3-95jq-q3rf. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-jfm3-95jq-q3rf in your dependencies?
O3 detects GHSA-jfm3-95jq-q3rf across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.