CVE-2026-27739 — @angular/ssr
Fix: angular/angular-cli#32516CVE-2026-27739 is a Server-Side Request Forgery (SSRF) vulnerability in @angular/ssr. A fix is available for @angular/ssr — see the affected versions and patch details below.
Angular SSR is vulnerable to SSRF and Header Injection via request handling pipeline
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27739.
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.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@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.1npm install @angular/ssr@21.2.0-rc.1 |
| 📦npm | @angular/ssr | ≥ 21.0.0-next.0&&< 21.1.5 | 21.1.5npm install @angular/ssr@21.1.5 |
| 📦npm | @angular/ssr | ≥ 20.0.0-next.0&&< 20.3.17 | 20.3.17npm install @angular/ssr@20.3.17 |
| 📦npm | @angular/ssr | all versions | 19.2.21npm install @angular/ssr@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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-27739 can be triaged on real exposure rather than presence alone.
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 Security finds CVE-2026-27739 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.