GHSA-mh2x-fcqh-fmqv
MEDIUM@sveltejs/kit has unescaped error message included on error page
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
@sveltejs/kitnpmDescription
Summary
The static error.html template for errors contains placeholders that are replaced without escaping the content first.
Details
From https://kit.svelte.dev/docs/errors:
error.html is the page that is rendered when everything else fails. It can contain the following placeholders: %sveltekit.status% — the HTTP status %sveltekit.error.message% — the error message
This leads to possible injection if an app explicitly creates an error with a message that contains user controlled content that ends up being something like this inside a server handle function:
error(500, '<script>alert("boom")</script>');
Uncaught errors cannot be exploited like this, as they always render the message "Internal error".
Escaping the message string in the function that creates the html output can be done to improve safety for applications that are using custom errors on the server.
PoC
None provided
Impact
Only applications where user provided input is used in the Error message will be vulnerable, so the vast majority of applications will not be vulnerable
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @sveltejs/kit | all versions | 2.8.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @sveltejs/kit. 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 @sveltejs/kit to 2.8.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mh2x-fcqh-fmqv 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-mh2x-fcqh-fmqv 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-mh2x-fcqh-fmqv. 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-mh2x-fcqh-fmqv in your dependencies?
O3 detects GHSA-mh2x-fcqh-fmqv across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.