GitHub Security Advisory: GHSA-x288-3778-4hhx
Package: @angular/ssr (NPM)
Severity: CRITICAL (CVSS 0.0)
CWE: CWE-918: Server-Side Request Forgery (SSRF)
Vulnerable versions: >= 20.0.0-next.0, < 20.3.17
Patched in: 20.3.17

Summary: Angular SSR is vulnerable to SSRF and Header Injection via request handling pipeline

Details:
A [Server-Side Request Forgery (SSRF)](https://developer.mozilla.org/en-US/docs/Web/Security/Attacks/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, us