GHSA-vfrc-7r7c-w9mx is a medium-severity (CVSS 5.8) CWE-471 vulnerability in highlight.js. O3 Security confirms whether GHSA-vfrc-7r7c-w9mx is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Prototype Pollution in highlight.js
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
highlight.jsnpmDescription
Impact
Affected versions of this package are vulnerable to Prototype Pollution. A malicious HTML code block can be crafted that will result in prototype pollution of the base object's prototype during highlighting. If you allow users to insert custom HTML code blocks into your page/app via parsing Markdown code blocks (or similar) and do not filter the language names the user can provide you may be vulnerable.
The pollution should just be harmless data but this can cause problems for applications not expecting these properties to exist and can result in strange behavior or application crashes, i.e. a potential DOS vector.
If your website or application does not render user provided data it should be unaffected.
Patches
Versions 9.18.2 and 10.1.2 and newer include fixes for this vulnerability. If you are using version 7 or 8 you are encouraged to upgrade to a newer release.
Workarounds
Patch your library
Manually patch your library to create null objects for both languages and aliases:
const HLJS = function(hljs) {
// ...
var languages = Object.create(null);
var aliases = Object.create(null);
Filter out bad data from end users:
Filter the language names that users are allowed to inject into your HTML to guarantee they are valid.
References
For more information
If you have any questions or comments about this advisory:
- Please file an issue against highlight.js
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | highlight.js | all versions | 9.18.2 |
| 📦npm | highlight.js | ≥ 10.0.0&&< 10.1.2 | 10.1.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for highlight.js. 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 highlight.js to 9.18.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-vfrc-7r7c-w9mx 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-vfrc-7r7c-w9mx 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-vfrc-7r7c-w9mx. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
In Red Hat Virtualization, ovirt-engine-api-explorer uses a vulnerable version of highlight.js, however since release 4.4.3 ovirt-engine-api-explorer is obsoleted and no longer used.
Frequently Asked Questions
Is GHSA-vfrc-7r7c-w9mx in your dependencies?
O3 detects GHSA-vfrc-7r7c-w9mx across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.