CVE-2026-27739 Angular SSR is vulnerable to SSRF and Header Injection via request handling pipeline
Attackers can exploit unvalidated headers in Angular SSR to perform Server-Side Request Forgery, enabling internal network probing and credential exfiltration.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-27739?
CVE-2026-27739 is a critical server-side request forgery vulnerability in angular @nguniversal/common, published on 25 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
The Angular SSR is a server-rise rendering tool for Angular applications. Versions prior to 21.2.0-rc.1, 21.1.5, 20.3.17, and 19.2.21 have a Server-Side Request Forgery (SSRF) vulnerability 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 host domain, path and character sanitization, and port validation. This vulnerability manifests in two primary ways: implicit relative URL resolution and explicit manual construction. When successfully exploited, this vulnerability allows for arbitrary internal request steering. This can lead to credential exfiltration, internal network probing, and a confidentiality breach. In order to be vulnerable, 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, the application server must be reachable by an attacker who can influence these headers without strict validation from a front-facing proxy, and the infrastructure (Cloud, CDN, or Load Balancer) must not sanitize or validate incoming headers. Versions 21.2.0-rc.1, 21.1.5, 20.3.17, and 19.2.21 contain a patch. Some workarounds are available. Avoid using `req.headers` for URL construction. Instead, use trusted variables for base API paths. Those who cannot upgrade immediately should implement a middleware in their `server.ts` to enforce numeric ports and validated hostnames.
Weakness: CWE-918
Which versions are affected by CVE-2026-27739?
12 open source packages ship an affected version, including @angular/ssr, @nguniversal/common and @nguniversal/express-engine.
| Package | Affected | Fixed in |
|---|---|---|
@angular/ssr npm | All versions | 19.2.21 |
@angular/ssr npm | All versions | 19.2.21 |
@angular/ssr npm | From 20.0.0-next.0 | 20.3.17 |
@angular/ssr npm | From 20.0.0-next.0 | 20.3.17 |
@angular/ssr npm | From 21.0.0-next.0 | 21.1.5 |
@angular/ssr npm | From 21.0.0-next.0 | 21.1.5 |
6 more packages
@angular/ssr npm | From 21.2.0-next.0 | 21.2.0-rc.1 |
@angular/ssr npm | From 21.2.0-next.0 | 21.2.0-rc.1 |
@nguniversal/common npm | All versions to 16.2.0 | None |
@nguniversal/common npm | All versions to 16.2.0 | None |
@nguniversal/express-engine npm | All versions to 16.2.0 | None |
@nguniversal/express-engine npm | All versions to 16.2.0 | None |
How do I fix CVE-2026-27739?
Upgrade @angular/ssr to a fixed version for your release line: 19.2.21, 20.3.17, 21.1.5 or 21.2.0-rc.1.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-27739 being exploited?
There is no known exploitation of CVE-2026-27739 in the wild and no public exploit code.
Public exploit code: 2 proofs of concept on GitHub.
Sources
Also known as CLSA-2026-1776645366, CLSA-2026-1776645367, CLSA-2026-1778460307, CLSA-2026-1792163460, CLSA-2026-1792163461, CLSA-2026-1792202606 and 16 more.