Angular: SSR XSS via Unescaped <template> Content Across DocumentFragment Boundaries in Fallback Raw-Content Elements

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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 untrusted input inside template content nested in fallback raw-content elements such as noscript, iframe, noembed, and noframes. The Domino serializer's fallbackRawContentTags traversal stopped at the DocumentFragment used by template.content, so matching closing tags in xmp, style, script, comments, or text nodes were not escaped. Standard interpolation with comments or text nodes is reachable without relaxed schemas; literal xmp or style requires CUSTOM_ELEMENTS_SCHEMA or NO_ERRORS_SCHEMA, while Renderer2 imperative DOM construction is unconditionally affected. When HTML5 RAWTEXT browser parsing encounters the unescaped closing tag, it exits the fallback container and interprets trailing markup as active DOM elements, enabling arbitrary JavaScript execution. This issue is fixed in versions 20.3.30, 21.2.22, and 22.1.4.

Source published

10 Sep 2026 19:04:17 UTC

Source modified

10 Sep 2026 19:20:56 UTC

Saved here

23 Oct 2026 15:48:27 UTC

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CVE Program Terms of Use

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CVSS 4.0 · 8.6 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

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 untrusted input inside template content nested in fallback raw-content elements such as noscript, iframe, noembed, and noframes. The Domino serializer's fallbackRawContentTags traversal stopped at the DocumentFragment used by template.content, so matching closing tags in xmp, style, script, comments, or text nodes were not escaped. Standard interpolation with comments or text nodes is reachable without relaxed schemas; literal xmp or style requires CUSTOM_ELEMENTS_SCHEMA or NO_ERRORS_SCHEMA, while Renderer2 imperative DOM construction is unconditionally affected. When HTML5 RAWTEXT browser parsing encounters the unescaped closing tag, it exits the fallback container and interprets trailing markup as active DOM elements, enabling arbitrary JavaScript execution. This issue is fixed in versions 20.3.30, 21.2.22, and 22.1.4.

Source published

Sep 10, 2026, 7:04:17 PM (timezone not stated)

Source modified

Sep 10, 2026, 7:20:56 PM (timezone not stated)

Saved here

11 Nov 2026 17:03:31 UTC

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ENISA EUVD · source terms and attribution apply

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EUVD CVSS 4.0 · 8.6 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

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 untrusted input inside template content nested in fallback raw-content elements such as noscript, iframe, noembed, and noframes. The Domino serializer's fallbackRawContentTags traversal stopped at the DocumentFragment used by template.content, so matching closing tags in xmp, style, script, comments, or text nodes were not escaped. Standard interpolation with comments or text nodes is reachable without relaxed schemas; literal xmp or style requires CUSTOM_ELEMENTS_SCHEMA or NO_ERRORS_SCHEMA, while Renderer2 imperative DOM construction is unconditionally affected. When HTML5 RAWTEXT browser parsing encounters the unescaped closing tag, it exits the fallback container and interprets trailing markup as active DOM elements, enabling arbitrary JavaScript execution. This issue is fixed in versions 20.3.30, 21.2.22, and 22.1.4.

Source published

10 Sep 2026 19:17:42 UTC

Source modified

29 Sep 2026 18:44:06 UTC

Saved here

25 Oct 2026 16:19:22 UTC

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NIST NVD usage terms; underlying source attribution retained

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CVSS 4.0 · [email protected] · Secondary · 8.6 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS 3.1 · [email protected] · Primary · 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

### Summary An XSS vulnerability exists in `@angular/platform-server` during server-side rendering (SSR) HTML serialization when traversing ancestor tags across `<template>` element boundaries. When an application renders untrusted user input within raw-text tags (`<xmp>`, `<style>`, `<script>`), comments, or text nodes inside a `<template>` that is nested within a fallback raw-content element (`<noscript>`, `<iframe>`, `<noembed>`, `<noframes>`), matching closing tags (e.g., `</noscript>`) are not escaped during HTML serialization. When rendered in a browser, this unescaped closing tag prematurely terminates the fallback container and executes trailing markup as active DOM elements. ### Technical Description In HTML5 parsing, fallback raw-content elements (`<noscript>`, `<iframe>`, `<noembed>`, `<noframes>`) place the browser's tokenizer into `RAWTEXT` mode. In this mode, inner content is parsed as literal text until an end tag matching the container tag name (e.g., `</noscript>`) is encountered. To prevent XSS breakout vectors during SSR serialization, the DOM serializer inspects a node's ancestors to escape any matching fallback closing tags (`</tag` -> `&lt;/tag`). However: 1. Per DOM specifications, the children of a `<template>` element reside in a separate `DocumentFragment` (`template.content`), whose own `parentNode` is `null`. 2. The serializer's ancestor traversal previously only inspected element nodes. When traversing upward from a node inside `template.content`, traversal terminated immediately at the `DocumentFragment` boundary. 3. Because traversal stopped before reaching the outer document tree, enclosing fallback raw-content ancestors (such as `<noscript>` or `<iframe>`) were not discovered. As a result, closing sequences like `</noscript>` within `<template>` content were emitted unescaped. ### Impact & Reachability * **Framework Guarantee Bypass**: Angular guarantees that standard text interpolation (`{{ userInput }}` bound as element text content) is safe by default without manual sanitization. This vulnerability bypasses that guarantee during SSR HTML serialization when untrusted input is interpolated inside template content within fallback containers. * **Template Authoring**: Writing literal `<xmp>` or `<style>` directly inside a component's `<template>` markup requires relaxed template schema checks (`CUSTOM_ELEMENTS_SCHEMA` or `NO_ERRORS_SCHEMA`). However, standard HTML comments and text nodes inside `<template>` within `<noscript>` are reachable without relaxed schemas. * **Imperative DOM Construction**: Components or directives that construct DOM structures imperatively via `Renderer2` bypass template compiler schema checks entirely and are unconditionally affected. ### Proof of Concept (Minimal Reproduction) ```ts import { Component } from '@angular/core'; @Component({ selector: 'app-root', standalone: true, template: ` <noscript> <template> <xmp>{{ payload }}</xmp> </template> </noscript> ` }) export class AppComponent { // Attacker-controlled input bound via standard text interpolation payload = '</noscript><img src=x onerror=alert("SSR_TEMPLATE_XSS")>'; } ``` **Vulnerable SSR Output**: ```html <noscript><template><xmp></noscript><img src=x onerror=alert("SSR_TEMPLATE_XSS")></xmp></template></noscript> ``` ### Workarounds * Avoid rendering untrusted user input inside `<template>` elements nested within `<noscript>`, `<iframe>`, `<noembed>`, or `<noframes>` in server-rendered templates. * Avoid programmatic DOM assembly of `<template>` elements inside fallback containers when handling untrusted data.

Source published

10 Sep 2026 20:25:25 UTC

Source modified

25 Sep 2026 05:30:06 UTC

Saved here

24 Oct 2026 13:17:17 UTC

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GitHub Advisory Database · CC-BY-4.0

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CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Publisher rating · HIGH