CVE-2026-27739: Angular SSR Vulnerable to SSRF and Header Injection

Background

Angular SSR (Server-Side Rendering) is a framework that allows developers to render Angular applications on the server, enhancing performance and SEO. It processes incoming requests and generates HTML responses, making it essential for applications that require fast initial load times and better search engine visibility. However, a critical vulnerability has been identified in its request handling pipeline, exposing applications to potential attacks.

Vulnerability Detail

A Server-Side Request Forgery (SSRF) vulnerability exists in Angular SSR due to its internal URL reconstruction logic, which improperly trusts user-controlled HTTP headers like Host and X-Forwarded-* without validating the destination domain. This oversight allows attackers to manipulate the application's base origin, leading to potential credential exfiltration, internal network probing, and confidentiality breaches. The vulnerability arises from the lack of checks on Host Domain, Path & Character Sanitization, and Port Validation, making it possible for attackers to redirect requests to malicious servers or internal services.

npm install @angular/ssr@22.2.4

Workaround

If immediate upgrading is not possible, implement strict header validation in your server code. Below is a middleware example to enforce numeric ports and validated hostnames:

const ALLOWED_HOSTS = 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];
    if (/^[a-z0-9.:-]+$/i.test(hostname) || (!ALLOWED_HOSTS.has(hostname) && hostname !== 'localhost')) {
      return res.status(400).send('Invalid Hostname');
    }
  }

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

next();

});

Conclusion

The identified SSRF and Header Injection vulnerability in Angular SSR poses significant risks to applications using this framework. It is crucial to update to the latest patched versions or implement strict header validation to mitigate potential attacks. Regular monitoring with tools like Vulert can help maintain security against such vulnerabilities.

See every vulnerability recorded for @angular/ssr →

FAQ