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

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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.

Source published

10 Sep 2026 18:56:03 UTC

Source modified

11 Sep 2026 15:14:37 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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 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.

Source published

Sep 10, 2026, 6:56:03 PM (timezone not stated)

Source modified

Sep 11, 2026, 3:14:37 PM (timezone not stated)

Observed here

11 Nov 2026 17:03:28 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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 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.

Source published

10 Sep 2026 19:17:41 UTC

Source modified

29 Sep 2026 19:01:24 UTC

Observed here

25 Oct 2026 16:19:22 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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 of `ProcessingInstruction` DOM nodes (`<?target data?>`, `nodeType === 7`) when nested inside fallback raw-content elements (`<noscript>`, `<iframe>`, `<noembed>`, `<noframes>`). While processing instruction data escaped `>` to `&gt;`, it did not check for or escape matching closing tags of ancestor fallback elements (e.g., `</noscript>`). When rendered in a browser with scripting enabled, an unescaped closing tag sequence in a processing instruction prematurely closes the fallback raw-content tag and causes subsequent sibling elements to execute as live HTML. ### Technical Description In HTML5 parsing, fallback raw-content elements (`<noscript>`, `<iframe>`, `<noembed>`, `<noframes>`) place the browser's HTML tokenizer into `RAWTEXT` mode. In `RAWTEXT` mode, processing instruction tokens (`<?...?>`) are treated as literal raw text rather than bogus comments, and the parser ignores `>` or `?>`. The only token sequence that terminates the container is an end tag matching the container tag name (`</noscript`, `</iframe`, etc.). During server-side HTML serialization, processing instruction nodes previously only replaced `>` with `&gt;` (preventing bogus comment breakouts in normal HTML data states) but left `<` untouched. Crucially, processing instruction serialization never inspected ancestor fallback raw-content tags. As a result, if a `ProcessingInstruction` node inside `<noscript>` contained `</noscript ` in its data payload, it was emitted unescaped as `<?x </noscript ?>`. ### Impact & Reachability * **Reachability**: Processing instruction nodes cannot be authored directly through standard Angular template syntax (which parses `<?...>` into comment nodes in DOM position). Reaching this vulnerability requires application or library code calling `inject(DOCUMENT).createProcessingInstruction(target, data)` or `Renderer2` DOM insertion methods with untrusted user input passed to `data` inside a fallback raw-content container. * **Impact**: In applications that programmatically construct processing instruction nodes inside fallback elements during server-side rendering, an attacker controlling the processing instruction data can break out of the container and execute arbitrary JavaScript in victims' browsers. ### Proof of Concept (Minimal Reproduction) ```ts import { Component, ElementRef, Renderer2, inject, DOCUMENT, AfterViewInit } from '@angular/core'; @Component({ selector: 'app-root', standalone: true, template: `<noscript id="host"></noscript>` }) export class AppComponent implements AfterViewInit { private r = inject(Renderer2); private el = inject(ElementRef); private doc = inject(DOCUMENT); ngAfterViewInit() { const host = this.el.nativeElement.querySelector('#host'); // Attacker-controlled input passed as Processing Instruction data const pi = this.doc.createProcessingInstruction('x', '</noscript '); this.r.appendChild(host, pi); // Sibling markup that should remain inert inside <noscript> const img = this.r.createElement('img'); this.r.setAttribute(img, 'src', 'x'); this.r.setAttribute(img, 'onerror', 'alert("SSR_PI_XSS")'); this.r.appendChild(host, img); } } ``` **Vulnerable SSR Output**: ```html <noscript><?x </noscript ?><img src="x" onerror="alert('SSR_PI_XSS')"></noscript> ``` ### Workarounds * Avoid passing untrusted user input into `document.createProcessingInstruction(target, data)` when the node is inserted into `<noscript>`, `<iframe>`, `<noembed>`, or `<noframes>` during server-side rendering. * Manually sanitize or replace `<` with `&lt;` in any untrusted data passed to processing instruction nodes on the server.

Source published

28 Sep 2026 20:39:26 UTC

Source modified

28 Sep 2026 20:45:04 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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