CVE-2026-101896: Angular Server-Side Rendering (SSR): Denial of Service via Numeric URL Matrix Parameters

A denial of service (DoS) vulnerability was identified in `@angular/router` when Server-Side Rendering (SSR) is enabled on Node.js (V8). When `@angular/router` parses incoming request URLs, it extracts path segments, matrix parameters, and child outlets into plain JavaScript objects (`Record<string, string>`). When matrix parameter names or outlet names are numeric strings (such as `/a;990;2522`), the V8 JavaScript engine interprets them as array-indexed properties rather than named properties. Under V8's internal property-storage heuristics, setting numeric keys on an initially empty object causes V8 to allocate a dense array backing store (`HOLEY_ELEMENTS`) sized to the maximum index rather than falling back to sparse dictionary storage. Specifically, assigning sequential or moderately large numeric keys (like `990` followed by `2522`) causes V8 to allocate a contiguous backing store of ~2,522 pointers (~20 KB to 25 KB of heap) for a single 11-byte segment. Because each segment in a URL path allocates its own independent `parameters` object, an attacker can craft URLs with repeated numeric matrix parameters to achieve an asymmetric memory amplification factor of approximately **~350x**. ### Impact Successful exploitation allows an unauthenticated remote attacker to exhaust the Node.js old-space heap with modest request volume, terminating the SSR worker with an unrecoverable `JavaScript heap out of memory` fatal error and causing a Denial of Service. * **High Amplification:** A single 11-byte segment (`/a;990;2522`) consumes ~20 KB–25 KB of V8 heap. * **Low Concurrency Required:** * With 8 KB request paths (~740 segments, within default Nginx 8 KB buffer limits), as few as **12–22 concurrent requests** crash a 256 MiB–512 MiB Node.js SSR worker. * With smaller 1 KB–2 KB request paths (~90–180 segments), a burst of ~50–100 concurrent requests achieves the same heap exhaustion. * **Client-side SPAs Unaffected:** Pure client-side Angular applications (Single Page Applications without SSR) are **not** vulnerable, as local browser memory consumption does not cross a security boundary. ### Attack Preconditions & Vulnerable Configurations An application is affected only if **all** of the following conditions are met: * **SSR Enabled:** The application runs in a Server-Side Rendering environment powered by Node.js / V8. * **Direct Router Parsing:** User-controlled request URLs are parsed by `@angular/router` during SSR. * **No Reverse-Proxy Semicolon/Segment Filtering:** Upstream reverse proxies (Nginx, Cloudflare, ALB) forward URLs containing semicolons (`;`) and multiple path segments without stripping or rejecting them. #### Exploit Payload Example An attacker sends concurrent HTTP requests with repeated numeric matrix parameters: ```http GET /a;990;2522/a;990;2522/a;990;2522/... HTTP/1.1 Host: example.com ``` Even with paths under 2 KB, overlapping requests during SSR will rapidly consume the V8 heap until the process crashes. ### Patches The issue is resolved by updating `@angular/router` to enforce V8 dictionary elements storage (`setUrlDerivedKey`) for numeric URL-derived keys (index >= 32). This prevents V8 from allocating oversized contiguous array backing stores while preserving route matching, parameter values, and component input bindings. * `22.2.0` * `21.2.24` * `20.3.32` ### Workarounds & Mitigations If you cannot immediately upgrade to a patched version, apply one of the following mitigations at your edge or reverse proxy: 1. **Block or Sanitize Matrix Parameters at the Reverse Proxy:** Configure your reverse proxy (e.g., Nginx, Cloudflare, or AWS WAF) to reject or strip semicolons (`;`) in request paths before forwarding requests to the Angular SSR service: ```nginx # Nginx example: reject requests containing matrix parameters if ($uri ~* ";") { return 400; } ``` 2. **Enforce Strict Path Segment Limits:** Reject requests with excessive path depth (e.g., more than 20–30 segments). 3. **Increase Node.js Old Space:** Increase `--max-old-space-size` (e.g., to 2048 or 4096 MB) to increase the concurrency threshold required to exhaust memory, though this does not fully eliminate the vulnerability under sustained traffic.