Angular SSR: Denial of Service (DoS) via Infinite Loop on Malformed DOCTYPE

Summary

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.

Timeline

1. Oct 14, 2026, 3:00 PM UTCCVE published
2. Oct 14, 2026, 5:37 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: yes · Technical impact: partial

3. Oct 14, 2026, 5:38 PM UTCRecord last updated

Affected versions

• angular angular

  through 19.2.25; From 20.0.0 · fixed in 20.3.31; From 21.0.0 · fixed in 21.2.23; From 22.0.0 · fixed in 22.1.6

• @angular/ platform-server

  through 19.2.25; From 20.0.0 · fixed in 20.3.31; From 21.0.0 · fixed in 21.2.23; From 22.0.0 · fixed in 22.1.6

• @angular/platform-servernpm

  From 22.0.0 · fixed in 22.1.6

• @angular/platform-servernpm

  From 21.0.0 · fixed in 21.2.23

• @angular/platform-servernpm

  From 20.0.0 · fixed in 20.3.31

• @angular/platform-servernpm

  through 19.2.25

References 7