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fix(@angular/build): escape hostname in host-validation 403 error page #33673

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deprrous wants to merge 1 commit into from
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fix(@angular/build): escape hostname in host-validation 403 error page #33673

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14 changes: 12 additions & 2 deletions packages/angular/build/src/tools/vite/middlewares/host-check-middleware.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,17 @@ export function patchHostValidationMiddleware(middlewares: Connect.Server): void
};
}

function escapeHtml(value: string): string {
return value
.replace(/&/g, '&')
.replace(/</g, '&lt;')
.replace(/>/g, '&gt;')
.replace(/"/g, '&quot;');
}
Comment on lines +45 to +51

@gemini-code-assist gemini-code-assist Bot Jul 29, 2026

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medium

The current implementation of escapeHtml uses multiple chained .replace calls with regular expressions, which results in multiple string allocations and full-string scans. Additionally, it does not escape the single quote ('), which is a standard HTML entity that should be escaped to prevent potential XSS vulnerabilities in attribute contexts.

Using a single regular expression with a character class and a map lookup is more efficient and allows us to easily include the single quote (') in the escaped characters.

function escapeHtml(value: string): string {
  const entityMap: Record<string, string> = {
    '&': '&amp;',
    '<': '&lt;',
    '>': '&gt;',
    '"': '&quot;',
    "'": '&#39;',
  };
  return value.replace(/[&<>"']/g, (s) => entityMap[s]);
}


function html403(hostname: string): string {
const safeHostname = escapeHtml(hostname);

return `<!doctype html>
<html>
<head>
Expand All @@ -61,12 +71,12 @@ function html403(hostname: string): string {
</head>
<body>
<main>
<h1>Blocked request. This host ("${hostname}") is not allowed.</h1>
<h1>Blocked request. This host ("${safeHostname}") is not allowed.</h1>
<p>To allow this host, add it to <code>allowedHosts</code> under the <code>serve</code> target in <code>angular.json</code>.</p>
<pre><code>{
"serve": {
"options": {
"allowedHosts": ["${hostname}"]
"allowedHosts": ["${safeHostname}"]
}
}
}</code></pre>
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