CVE-2021-21306 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in marked. O3 Security confirms whether CVE-2021-21306 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Regular Expression Denial of Service (REDoS) in Marked
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
markednpmDescription
Marked is an open-source markdown parser and compiler (npm package "marked"). In marked from version 1.1.1 and before version 2.0.0, there is a Regular expression Denial of Service vulnerability. This vulnerability can affect anyone who runs user generated code through marked. This vulnerability is fixed in version 2.0.0.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | marked | ≥ 1.1.1&&< 2.0.0 | 2.0.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for marked. 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 marked to 2.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21306 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 CVE-2021-21306 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 CVE-2021-21306. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-21306 in your dependencies?
O3 detects CVE-2021-21306 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.