GHSA-3x58-xr87-2fcj is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in github.com/microcosm-cc/bluemonday. O3 Security confirms whether GHSA-3x58-xr87-2fcj is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Cross-site scripting in bluemonday
Real-World Exposure
github.com/microcosm-cc/bluemondayReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
bluemonday before 1.0.5 allows XSS because certain Go lowercasing converts an uppercase Cyrillic character, defeating a protection mechanism against the "script" string.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/microcosm-cc/bluemonday | all versions | 1.0.5 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/microcosm-cc/bluemonday. 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 github.com/microcosm-cc/bluemonday to 1.0.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-3x58-xr87-2fcj 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-3x58-xr87-2fcj 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-3x58-xr87-2fcj. 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-3x58-xr87-2fcj in your dependencies?
O3 detects GHSA-3x58-xr87-2fcj across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.