fix(platform): Sanitise next in platform-redirect

app/platform-redirect/page.tsx

@@ -8,6 +8,8 @@ import {SmartLink} from 'sentry-docs/components/smartLink';
 import {extractPlatforms, getDocsRootNode, nodeForPath} from 'sentry-docs/docTree';
 import {setServerContext} from 'sentry-docs/serverContext';
 
+import {sanitizeNext} from './utils';
+
 export const metadata: Metadata = {
   robots: 'noindex',
   title: 'Platform Specific Content',
@@ -27,8 +29,7 @@ export default async function Page(props: {
     next = next[0];
   }
 
-  // discard the hash
-  const [pathname, _] = next.split('#');
+  const pathname = sanitizeNext(next);
   const rootNode = await getDocsRootNode();
   const defaultTitle = 'Platform Specific Content';
   let description = '';
@@ -64,7 +65,7 @@ export default async function Page(props: {
       p => p.key === requestedPlatform?.toLowerCase()
     );
     if (isValidPlatform) {
-      return redirect(`/platforms/${requestedPlatform}${next}`);
+      return redirect(`/platforms/${requestedPlatform}${pathname}`);
     }
   }
 
@@ -83,7 +84,7 @@ export default async function Page(props: {
       <ul>
         {platformList.map(p => (
           <li key={p.key}>
-            <SmartLink to={`/platforms/${p.key}${next}`}>
+            <SmartLink to={`/platforms/${p.key}${pathname}`}>
               <PlatformIcon
                 size={16}
                 platform={p.icon ?? p.key}

app/platform-redirect/utils.spec.ts

@@ -0,0 +1,46 @@
+import {describe, expect, it} from 'vitest';
+
+import {sanitizeNext} from './utils';
+
+describe('sanitizeNext', () => {
+  it('should return an empty string for external URLs', () => {
+    expect(sanitizeNext('http://example.com')).toBe('');
+    expect(sanitizeNext('https://example.com')).toBe('');
+    expect(sanitizeNext('//example.com')).toBe('');
+  });
+
+  it('should prepend a slash if missing', () => {
+    expect(sanitizeNext('path/to/resource')).toBe('/path/to/resource');
+  });
+
+  it('should not modify a valid internal path', () => {
+    expect(sanitizeNext('/path/to/resource')).toBe('/path/to/resource');
+  });
+
+  it('should remove unsafe characters', () => {
+    expect(sanitizeNext('/path/to/resource?query=1')).toBe('/path/to/resource');
+    expect(sanitizeNext('/path/to/resource#hash')).toBe('/path/to/resource');
+  });
+
+  it('should allow alphanumeric and hyphens', () => {
+    expect(sanitizeNext('/path-to/resource123')).toBe('/path-to/resource123');
+  });
+
+  it('should return an empty string for paths with colons', () => {
+    expect(sanitizeNext('/path:to/resource')).toBe('');
+  });
+
+  it('should return an empty string for the root path', () => {
+    expect(sanitizeNext('/')).toBe('');
+  });
+
+  it('should decode URL encoded characters', () => {
+    expect(sanitizeNext('/path%2Fwith%2Fslashes')).toBe('/path/with/slashes');
+  });
+
+  it('should return an empty string for a malformed URI component', () => {
+    const input = '%E0%A4%A'; // Malformed URI
+    const expectedOutput = '';
+    expect(sanitizeNext(input)).toBe(expectedOutput);
+  });
+});

app/platform-redirect/utils.ts

@@ -0,0 +1,33 @@
+export const sanitizeNext = (next: string) => {
+  // Safely decode URI component
+  let sanitizedNext: string;
+  try {
+    sanitizedNext = decodeURIComponent(next);
+  } catch (e) {
+    // Return empty string if decoding fails
+    return '';
+  }
+
+  // Validate that next is an internal path
+  if (
+    sanitizedNext.startsWith('//') ||
+    sanitizedNext.startsWith('http') ||
+    sanitizedNext.includes(':')
+  ) {
+    // Reject potentially malicious redirects
+    sanitizedNext = '';
+  }
+
+  // Ensure next starts with a forward slash and only contains safe characters
+  if (sanitizedNext && !sanitizedNext.startsWith('/')) {
+    sanitizedNext = '/' + sanitizedNext;
+  }
+
+  // Discard hash and path parameters
+  const [pathname] = sanitizedNext.split('#')[0].split('?');
+
+  // Only allow alphanumeric, hyphens
+  sanitizedNext = pathname.replace(/[^\w\-\/]/g, '');
+
+  return sanitizedNext === '/' ? '' : sanitizedNext;
+};