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

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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 20.3.31, 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.

Source published

14 Oct 2026 15:00:14 UTC

Source modified

14 Oct 2026 17:38:10 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 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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 20.3.31, 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.

Source published

Oct 14, 2026, 3:00:14 PM (timezone not stated)

Source modified

Oct 14, 2026, 5:38:10 PM (timezone not stated)

Observed here

9 Nov 2026 04:16:01 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 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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 20.3.31, 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.

Source published

14 Oct 2026 15:17:03 UTC

Source modified

16 Oct 2026 16:00:33 UTC

Observed here

25 Oct 2026 04:17:26 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 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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

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 `after_doctype_name_state` (`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 `after_doctype_name_state` 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`.

Source published

28 Sep 2026 21:31:21 UTC

Source modified

28 Sep 2026 21:45:03 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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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: 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:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Publisher rating · HIGH