Angular: SSR XSS via Unescaped Processing Instruction (<?...?>) Nodes in Fallback Raw-Content Elements

Summary

Angular is a development platform for building mobile and desktop web applications using TypeScript/JavaScript and other languages. Prior to 20.3.30, 21.2.22, and 22.1.4, Angular server-side rendering (SSR) in @angular/platform-server serializes ProcessingInstruction DOM nodes inside fallback raw-content elements without escaping matching ancestor closing tags. ProcessingInstruction data escaped greater-than characters but left less-than characters untouched and did not inspect fallback ancestors, so data such as a matching closing tag prematurely terminates noscript, iframe, noembed, or noframes containers. The vulnerable nodes cannot be authored through standard Angular templates; reachability requires application or library code using inject(DOCUMENT).createProcessingInstruction with attacker-controlled data or Renderer2 DOM insertion inside a fallback container. In HTML5 RAWTEXT parsing, the premature close causes subsequent sibling elements to be interpreted as live HTML and enables arbitrary JavaScript execution in a victim's browser. This issue is fixed in versions 20.3.30, 21.2.22, and 22.1.4.

Timeline

1. Sep 10, 2026, 6:56 PM UTCCVE published
2. Sep 11, 2026, 3:14 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: total

3. Sep 11, 2026, 3:14 PM UTCRecord last updated

Affected versions

• angular angular

  through 19.2.25; From 20.0.0 · fixed in 20.3.30; From 21.0.0 · fixed in 21.2.22; From 22.0.0 · fixed in 22.1.4

• @angular/platform-servernpm

  From 22.0.0 · fixed in 22.1.4

• @angular/platform-servernpm

  From 21.0.0 · fixed in 21.2.22

• @angular/platform-servernpm

  From 20.0.0 · fixed in 20.3.30

• @angular/platform-servernpm

  through 19.2.25

References 9