Angular is a development platform for building mobile and desktop web applications using TypeScript/JavaScript and other languages. Prior to 22.0.0-rc.2, 21.2.16, 20.3.24, and 19.2.25, a Cross-Site Scripting (XSS) vulnerability exists in @angular/platform-server's DOM emulation dependency (domino) when serializing the content of <noscript> elements. When rendering dynamic text content inside a <noscript> element via template bindings (such as {{ value }} or [textContent]), the template engine expects the browser to render the content safely. Under Server-Side Rendering (SSR), domino is configured with scripting enabled, meaning <noscript> is treated as a raw-text element. However, domino's serializer completely omitted <noscript> from the list of raw-text elements requiring closing-tag escaping during DOM serialization. As a result, any occurrence of </noscript> in the bound dynamic text was never escaped under any circumstances. The unescaped closing tag was serialized directly into the output HTML (e.g. <noscript></noscript><script>alert(1)</script></noscript>). When parsed by a browser, it closes the <noscript> block early, allowing the injected <script> block to execute in the user's browser context, causing same-origin Cross-Site Scripting (XSS). This vulnerability is fixed in 22.0.0-rc.2, 21.2.16, 20.3.24, and 19.2.25.

Angular is a development platform for building mobile and desktop web applications using TypeScript/JavaScript and other languages. Prior to versions 19.2.21, 20.3.19, 21.2.9, and 22.0.0-next.8, a Server-Side Request Forgery (SSRF) vulnerability exists in @angular/platform-server due to improper handling of URLs during Server-Side Rendering (SSR). When an attacker sends a request such as GET /\evil.com/ HTTP/1.1 the server engine (Express, etc.) passes the URL string to Angular’s rendering functions. Because the URL parser normalizes the backslash to a forward slash for HTTP/HTTPS schemes, the internal state of the application is hijacked to believe the current origin is evil.com. This misinterpretation tricks the application into treating the attacker’s domain as the local origin. Consequently, any relative HttpClient requests or PlatformLocation.hostname references are redirected to the attacker controlled server, potentially exposing internal APIs or metadata services. This issue has been patched in versions 19.2.21, 20.3.19, 21.2.9, and 22.0.0-next.8.

A Server-Side Request Forgery (SSRF) vulnerability has been identified in the Angular SSR request handling pipeline. The vulnerability exists because Angular’s internal URL reconstruction logic directly trusts and consumes user-controlled HTTP headers specifically the Host and X-Forwarded- family to determine the application's base origin without any validation of the destination domain.

Specifically, the framework didn't have checks for the following: - Host Domain: The Host and X-Forwarded-Host headers were not checked to belong to a trusted origin. This allows an attacker to redefine the "base" of the application to an arbitrary external domain. - Path & Character Sanitization: The X-Forwarded-Host header was not checked for path segments or special characters, allowing manipulation of the base path for all resolved relative URLs. - Port Validation: The X-Forwarded-Port header was not verified as numeric, leading to malformed URI construction or injection attacks.

This vulnerability manifests in two primary ways:

- Implicit Relative URL Resolution: Angular's HttpClient resolves relative URLs against this unvalidated and potentially malformed base origin. An attacker can "steer" these requests to an external server or internal service. - Explicit Manual Construction: Developers injecting the REQUEST object to manually construct URLs (for fetch or third-party SDKs) directly inherit these unsanitized values. By accessing the Host / X-Forwarded- headers, the application logic may perform requests to attacker-controlled destinations or malformed endpoints.

Impact

When successfully exploited, this vulnerability allows for arbitrary internal request steering. This can lead to: - Credential Exfiltration: Stealing sensitive Authorization headers or session cookies by redirecting them to an attacker's server. - Internal Network Probing: Accessing and transmitting data from internal services, databases, or cloud metadata endpoints (e.g., 169.254.169.254) not exposed to the public internet. - Confidentiality Breach: Accessing sensitive information processed within the application's server-side context.

Attack Preconditions

- The victim application must use Angular SSR (Server-Side Rendering). - The application must perform HttpClient requests using relative URLs OR manually construct URLs using the unvalidated Host / X-Forwarded- headers using the REQUEST object. - Direct Header Access: The application server is reachable by an attacker who can influence these headers without strict validation from a front-facing proxy. - Lack of Upstream Validation: The infrastructure (Cloud, CDN, or Load Balancer) does not sanitize or validate incoming headers.

Patches

- 21.2.0-rc.1 - 21.1.5 - 20.3.17 - 19.2.21

Workarounds - Use Absolute URLs: Avoid using req.headers for URL construction. Instead, use trusted variables for your base API paths. - Implement Strict Header Validation (Middleware): If you cannot upgrade immediately, implement a middleware in your server.ts to enforce numeric ports and validated hostnames.

ts const ALLOWEDHOSTS = new Set(['your-domain.com']);

app.use((req, res, next) => { const hostHeader = (req.headers['x-forwarded-host'] ?? req.headers['host'])?.toString(); const portHeader = req.headers['x-forwarded-port']?.toString();

if (hostHeader) { const hostname = hostHeader.split(':')[0]; // Reject if hostname contains path separators or is not in allowlist if (/^[a-z0-9.:-]+$/i.test(hostname) || (!ALLOWEDHOSTS.has(hostname) && hostname !== 'localhost')) { return res.status(400).send('Invalid Hostname'); } }

// Ensure port is strictly numeric if provided if (portHeader && !/^\d+$/.test(portHeader)) { return res.status(400).send('Invalid Port'); }

next(); });

References

- Fix - Docs