{"id":"CVE-2026-111754","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-111754","summary":"@angular/platform-server: Open Redirect via Protocol-Relative URLs in Server-Side Rendering (SSR)","details":"An open redirect vulnerability was identified in `@angular/platform-server` when Server-Side Rendering (SSR) is enabled.\n\nWhen Angular SSR renders an incoming request, URL resolution and platform navigation are managed by `ServerPlatformLocation` using `resolveUrl` (or `parseUrl` in v20). While `resolveUrl` rejected protocol-relative URLs whose raw string directly started with `//`, this check ran *prior* to WHATWG URL normalization.\n\nWhen a request URL includes a popping dot-segment followed by multiple slashes (such as `/.//evil.test` or serialized from router route shapes like `/.;/(//evil.test)`), the input bypassed the initial `urlStr.startsWith('//')` check. Subsequent WHATWG URL parsing resolved the dot-segments and resulted in a `pathname` starting with `//` (`//evil.test`).\n\nConsequently, `ServerPlatformLocation` stored `pathname = '//evil.test'`. When `@angular/ssr` detected a mismatch between the rendered URL and the router's final location state, it emitted the unnormalized pathname into the HTTP `Location` response header, producing an HTTP 302 redirect with `Location: //evil.test`, which browsers resolve as a protocol-relative navigation off-origin.\n\n### Impact\n\nSuccessful exploitation allows an unauthenticated remote attacker to craft URLs that trick Angular SSR into redirecting users to an arbitrary external domain.\n\n* **Bypasses Application-Level Guards:** Common application-level validation routines (such as checking `!returnUrl.startsWith('//')` before invoking `router.navigateByUrl`) accept `/.//evil.test` or `/.;/(//evil.test)` as a safe relative path, allowing attackers to bypass redirect allowlists.\n* **Client-side SPAs Unaffected:** Pure client-side Angular applications (Single Page Applications without SSR) are **not** vulnerable, as `ServerPlatformLocation` is only utilized in server-side execution environments.\n\n### Attack Preconditions & Vulnerable Configurations\n\nAn application is affected if the following conditions are met:\n\n* **SSR Enabled:** The application runs in a Server-Side Rendering environment using `@angular/platform-server` and `@angular/ssr`.\n* **Parameter Route Shapes:** The router contains parameter routes with wildcard or child segments (e.g. `/:tenant` matching `.` and serializing secondary outlet groups `(//evil.test)` to `/.//evil.test`), or passes user-provided navigation targets (e.g. `returnUrl`).\n* **Reverse Proxy Passthrough:** Upstream reverse proxies (Nginx, Cloudflare, ALB) pass semicolons (`;`) or dot-segments without stripping or normalizing them.\n\n#### Exploit Payload Example\n\nAn attacker sends a request targeting a route with parameters and child segments:\n\n```http\nGET /.;/(//evil.test) HTTP/1.1\nHost: example.com\n```\n\n**Response:**\n```http\nHTTP/1.1 302 Found\nLocation: //evil.test\n```\n\nThe client browser resolves `//evil.test` protocol-relatively and redirects the user away from `example.com` to `evil.test`.\n\n### Patches\n\nThe issue is resolved by updating `resolveUrl` (and `parseUrl` in v20) in `@angular/platform-server` to verify that the normalized URL pathname does not start with `//` when `allowProtocolRelative` is `false`.\n\n* `22.2.1`\n* `21.2.25`\n* `20.3.33`\n\n### Workarounds & Mitigations\n\nIf you cannot immediately upgrade to a patched version, apply one of the following mitigations at your edge reverse proxy or WAF:\n\n1. **Reject Paths with Dot-Segments Followed by Slashes:**\n   Configure your reverse proxy (e.g., Nginx, Cloudflare, AWS WAF) to block requests containing `/.//`, `/..//`, or `/.;/`:\n   ```nginx\n   # Nginx example: reject suspicious path normalization sequences\n   if ($request_uri ~* \"(\\n/\\.\\/|\\/\\.\\;)\") {\n       return 400;\n   }\n   ```\n2. **Sanitize Redirect Headers:**\n   Ensure edge proxies or API gateways rewrite or disallow protocol-relative (`//`) `Location` response headers originating from the SSR upstream.","published":"2026-10-20T14:35:49Z","modified":"2026-10-20T14:45:03.771349618Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"@angular/platform-server","fixedVersion":"22.2.1"},{"ecosystem":"npm","name":"@angular/platform-server","fixedVersion":"21.2.25"},{"ecosystem":"npm","name":"@angular/platform-server","fixedVersion":"20.3.33"},{"ecosystem":"npm","name":"@angular/platform-server","fixedVersion":null}],"fix":{"url":"https://github.com/angular/angular/pull/71077","label":"angular/angular#71077"},"references":[{"type":"WEB","url":"https://github.com/angular/angular/security/advisories/GHSA-w739-gvwx-grc3"},{"type":"WEB","url":"https://github.com/angular/angular/pull/71077"},{"type":"WEB","url":"https://github.com/angular/angular/pull/71078"},{"type":"WEB","url":"https://github.com/angular/angular/pull/71079"},{"type":"WEB","url":"https://github.com/angular/angular/commit/450af9c813c7660b9bd91e5635f705ee3ed7b32a"},{"type":"WEB","url":"https://github.com/angular/angular/commit/83944fc8c50e86be90e8ec4184cd15002b5af262"},{"type":"WEB","url":"https://github.com/angular/angular/commit/928dcfd2582152655b5559509d057bf6a5a19521"},{"type":"WEB","url":"https://github.com/angular/angular/commit/d7d81e189d227108c3b9d39178dbb7389f6f970d"},{"type":"PACKAGE","url":"https://github.com/angular/angular"},{"type":"WEB","url":"https://github.com/angular/angular/releases/tag/v20.3.33"},{"type":"WEB","url":"https://github.com/angular/angular/releases/tag/v21.2.25"},{"type":"WEB","url":"https://github.com/angular/angular/releases/tag/v22.2.1"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-20T14:45:03.771349618Z"}}