Angular is a development platform for building mobile and desktop web applications using TypeScript/JavaScript and other languages. Prior to 20.3.31, 21.2.23, and 22.1.6, the @angular/platform-server DOM emulation parser can enter an infinite synchronous loop when Angular server-side rendering processes attacker-controlled HTML containing an incomplete DOCTYPE that ends with whitespace at end of input. In Domino lib/HTMLParser.js, after_doctype_name_state emits doctype and EOF tokens without advancing nextchar or leaving the fixed-lookahead state, so the scanner repeatedly handles the same EOF marker. A remote unauthenticated attacker can use this condition through server-side HTML parsing paths such as innerHTML binding to consume a Node.js SSR worker at full CPU, starve the event loop, and stop concurrent and subsequent requests. This issue is fixed in versions 20.3.31, 21.2.23, and 22.1.6.

Affected: npm: @angular/platform-server

A Denial of Service (DoS) vulnerability exists in `@angular/platform-server`'s DOM emulation parser (`domino`). When processing untrusted user input containing an incomplete DOCTYPE declaration ending with whitespace before EOF (such as `<!DOCTYPE html `), the HTML parser enters an infinite synchronous loop, pegging CPU utilization at 100% and completely freezing the Node.js server process.

### Technical Description In Angular Server-Side Rendering (SSR), `@angular/platform-server` uses `domino` to parse and sanitize HTML bound through template bindings (such as `[innerHTML]`) or manipulated via DOM APIs.

In Domino's HTML parser (`lib/HTMLParser.js`), tokenizer states that specify fixed lookahead—such as `after_doctype_name_state` (`lookahead = 6`)—rely on the state handler function to explicitly advance the character index pointer (`nextchar`). While branches for whitespace, `>`, and keyword matching advance `nextchar`, the EOF branch (`case -1: // EOF`) emitted doctype and EOF tokens without advancing `nextchar` or transitioning out of the state:

```javascript case -1: // EOF forcequirks(); emitDoctype(); emitEOF(); break; ```

Because `nextchar` remained unchanged pointing to the EOF marker character (`\uFFFF`), the scanner loop (`while (nextchar < numchars)`) repeatedly re-invoked `after_doctype_name_state` with `codepoint = EOF` indefinitely. In Node.js's single-threaded runtime, this synchronous loop starves the event loop entirely.

### Impact & Reachabilit…