Cloudanix VulnDB

CVE-2026-33397

Medium · 6.1

CVSS

6.1

EPSS

0.3%

Published

Mar 26, 2026

CISA due date

—

The record

The Angular SSR is a server-rise rendering tool for Angular applications. Versions on the 22.x branch prior to 22.0.0-next.2, the 21.x branch prior to 21.2.3, and the 20.x branch prior to 20.3.21 have an Open Redirect vulnerability in `@angular/ssr` due to an incomplete fix for CVE-2026-27738. While the original fix successfully blocked multiple leading slashes (e.g., `///`), the internal validation logic fails to account for a single backslash (`\`) bypass. When an Angular SSR application is deployed behind a proxy that passes the `X-Forwarded-Prefix` header, an attacker provides a value starting with a single backslash, the internal validation failed to flag the single backslash as invalid, the application prepends a leading forward slash, resulting in a `Location` header containing the URL, and modern browsers interpret the `/\` sequence as `//`, treating it as a protocol-relative URL and redirecting the user to the attacker-controlled domain. Furthermore, the response lacks the `Vary: X-Forwarded-Prefix` header, allowing the malicious redirect to be stored in intermediate caches (Web Cache Poisoning). Versions 22.0.0-next.2, 21.2.3, and 20.3.21 contain a patch. Until the patch is applied, developers should sanitize the `X-Forwarded-Prefix` header in their `server.ts` before the Angular engine processes the request.

Affected packages

Ecosystem Package Introduced Fixed
npm @angular/ssr 19.0.0-next.0 19.2.21
npm @angular/ssr 20.0.0-next.0 20.3.21
npm @angular/ssr 20.0.0-next.0 20.3.17
npm @angular/ssr 21.0.0-next.0 21.2.3
npm @angular/ssr 21.0.0-next.0 21.1.5
npm @angular/ssr 21.2.0-next.0 21.2.0-rc.1
npm @angular/ssr 22.0.0-next.0 22.0.0-next.2

Related vulnerabilities