CVE-2026-27739
Angular SSR is vulnerable to SSRF and Header Injection via request handling pipeline
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
@angular/ssrnpmDescription
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @angular/ssr | ≥ 21.2.0-next.0&&< 21.2.0-rc.1 | 21.2.0-rc.1 |
| 📦npm | @angular/ssr | ≥ 21.0.0-next.0&&< 21.1.5 | 21.1.5 |
| 📦npm | @angular/ssr | ≥ 20.0.0-next.0&&< 20.3.17 | 20.3.17 |
| 📦npm | @angular/ssr | all versions | 19.2.21 |
| 📦npm | @nguniversal/common | all versions | No fix |
| 📦npm | @nguniversal/express-engine | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @angular/ssr. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update @angular/ssr to 21.2.0-rc.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27739 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-27739 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-27739. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-27739 in your dependencies?
O3 detects CVE-2026-27739 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.