GHSA-6q87-84jw-cjhp
MEDIUM@sveltejs/kit vulnerable to Cross-site Scripting via tracked search_params
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
Unsanitized search param names cause XSS vulnerability. You are affected if you iterate over all entries of event.url.searchParams inside a server load function. Attackers can exploit it by crafting a malicious URL and getting a user to click a link with said URL.
Details
SvelteKit tracks which parameters in event.url.searchParams are read inside server load functions. If the application iterates over the these parameters, the uses.search_params array included in the boot script (embedded in the server-rendered HTML) will have any search param name included in unsanitized form.
packages/kit/src/runtime/server/utils.js:150 has the stringify_uses(node) function which prints these out.
Reproduction
In a +page.server.js or +layout.server.js:
/** @type {import('@sveltejs/kit').Load} */
export function load(event) {
const values = {};
for (const key of event.url.searchParams.keys()) {
values[key] = event.url.searchParams.get(key);
}
}
If a user visits the page in question via a link containing ?</script/><script>window.pwned%3D1</script/>, the </script> will be included verbatim in the payload, causing the embedded script to be executed.
It is not necessary to return the parameter value from load or render it in the page, only to read it (which causes it to be tracked as a dependency) while load is running.
Impact
Any application that iterates over all values in event.url.searchParams in a load function in +page.server.js or +layout.server.js (directly or indirectly) is vulnerable to XSS.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @sveltejs/kit | ≥ 2.0.0&&< 2.20.6 | 2.20.6 |
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 2.20.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-6q87-84jw-cjhp 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-6q87-84jw-cjhp 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-6q87-84jw-cjhp. 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-6q87-84jw-cjhp in your dependencies?
O3 detects GHSA-6q87-84jw-cjhp across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.