GHSA-mj63-m3rc-8ppr
MEDIUMGHSA-mj63-m3rc-8ppr is a medium-severity (CVSS 5.3) vulnerability in league/commonmark. O3 Security confirms whether GHSA-mj63-m3rc-8ppr is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
league/commonmark: Denial of service via deeply nested XML output
Blast Radius
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Description
Impact
XmlRenderer pretty-prints XML by emitting depth-proportional indentation whitespace for every opening and closing tag. For a tree of depth n, the indentation alone sums to O(n²) bytes of output (and corresponding memory), reachable through MarkdownToXmlConverter — e.g. str_repeat('> ', $depth) . "x\n", a single line of nested blockquotes — or through a direct XmlRenderer::renderDocument() call on an attacker-influenced AST.
This affects applications that convert untrusted Markdown to XML, which is an opt-in output path. The parser's max_nesting_level bounds the depth of parser-created trees, but its default is high enough to reach damaging sizes, can be raised by the host application, and does not constrain custom or programmatically built ASTs handed straight to the renderer. The result is a memory / output-size amplification rather than a hard crash, which is why this issue is rated Medium rather than High. No confidentiality or integrity impact. XML rendering was introduced in 2.0.0 (first shipped in 2.0.0-beta1, June 2021) and has emitted depth-proportional indentation ever since, so all 2.x releases are affected (verified against 2.8.x, clean upstream 1902f60f). 1.x has no XML renderer and is not affected.
Workarounds
Applications converting untrusted Markdown to XML should:
- Lower
max_nesting_levelto a conservative value appropriate to expected content, so the parser refuses to build extremely deep trees. This is the most direct lever for parser-produced ASTs, but does not protect trees built programmatically and passed straight toXmlRenderer. - Cap input size before conversion, since the amplification is driven by input-proportional depth.
- Constrain XML consumers with memory / output-size limits (and streaming or size caps on any downstream XML parser or storage) so one request cannot allocate unbounded output.
- Prefer HTML rendering for untrusted content where XML is not strictly required — the HTML renderer does not emit depth-proportional indentation and is not subject to this amplification.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | league/commonmark | ≥ 2.0.0&&< 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-mj63-m3rc-8ppr 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-mj63-m3rc-8ppr 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-mj63-m3rc-8ppr. 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-mj63-m3rc-8ppr in your dependencies?
O3 detects GHSA-mj63-m3rc-8ppr across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.