CVE-2026-101895: Npm/@angular/platform-server vulnerability
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 afterdoctypenamestate (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 afterdoctypenamestate with codepoint = EOF indefinitely. In Node.js's single-threaded runtime, this synchronous loop starves the event loop entirely.
Impact & Reachability Reachability: The vulnerability is reachable in any Angular SSR application where untrusted user input is bound to [innerHTML], interpolated into markup, or sanitized on the server. Impact: Successful exploitation allows an unauthenticated remote attacker to cause an immediate Denial of Service (DoS) by sending a payload containing an incomplete DOCTYPE (e.g., <!DOCTYPE html ). The Node.js SSR process locks up at 100% CPU and ceases responding to all concurrent and subsequent HTTP requests.
Proof of Concept: ts import { Component } from '@angular/core';
@Component({ selector: 'app-root', standalone: true, template: <div [innerHTML]="payload"></div>, }) export class AppComponent { // Attacker-controlled input containing an incomplete DOCTYPE ending with whitespace payload = '<!DOCTYPE html '; }
Workarounds Avoid binding untrusted user input directly to [innerHTML] in server-rendered templates; use standard text interpolation ({{ userInput }}) or [textContent] when raw HTML rendering is not required. Validate or sanitize user input before passing it to [innerHTML] on the server by stripping or rejecting strings matching /^<!DOCTYPE/i.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/@angular/platform-serverto a version that resolves this vulnerability.Fixed in 20.3.31 - Upgrade
Upgrade
npm/@angular/platform-serverto a version that resolves this vulnerability.Fixed in 21.2.23 - Upgrade
Upgrade
npm/@angular/platform-serverto a version that resolves this vulnerability.Fixed in 22.1.6 - Configuration
Avoid binding untrusted user input directly to [innerHTML] in server-rendered templates when raw HTML rendering is not required.
Angular SSR application Untrusted input HTML binding = Use standard text interpolation ({{ userInput }}) or [textContent] instead of [innerHTML] - Configuration
Validate or sanitize user input before passing it to [innerHTML] on the server by stripping or rejecting strings matching /^<!DOCTYPE/i.
Angular SSR application Server-side input validation/sanitization = Reject or strip strings matching /^<!DOCTYPE/i
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Angular Server-Side Rendering deployments using @angular/platform-server are exposed when they parse untrusted HTML through template bindings such as [innerHTML] or through DOM API manipulation.
What must an attacker supply to trigger the condition?
The attacker needs to cause the server to process HTML containing an incomplete DOCTYPE declaration that ends in whitespace at end of input, such as <!DOCTYPE html followed by a space and EOF.
What happens when the vulnerable parser is triggered?
The parser enters an infinite synchronous loop, drives CPU utilization to 100%, and freezes the Node.js server process.