CVE-2019-10905
HIGHCVE-2019-10905 is a high-severity (CVSS 8.1) Cross-site Scripting (XSS) vulnerability in erusev/parsedown. 1 public exploit reference exists, so weaponization risk is real. O3 Security confirms whether CVE-2019-10905 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Parsedown Class-Name Injection
Blast Radius
erusev/parsedownReal-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
Parsedown before 1.7.2, when safe mode is used and HTML markup is disabled, might allow attackers to execute arbitrary JavaScript code if a script (already running on the affected page) executes the contents of any element with a specific class. This occurs because spaces are permitted in code block infostrings, which interferes with the intended behavior of a single class name beginning with the language- substring.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | erusev/parsedown | all versions | 1.7.2 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for erusev/parsedown. 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 erusev/parsedown to 1.7.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-10905 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-2019-10905 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-2019-10905. 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-2019-10905 in your dependencies?
O3 detects CVE-2019-10905 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.