CVE-2026-101895: Angular SSR Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f67j-2jqw-jpq7",
  "modified" : "2026-09-28T21:31:21Z",
  "published" : "2026-09-28T21:31:21Z",
  "aliases" : [ "CVE-2026-101895" ],
  "summary" : "Angular SSR: Denial of Service (DoS) via Infinite Loop on Malformed DOCTYPE",
  "details" : "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.\n\n### Technical Description\nIn 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.\n\nIn 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:\n\n```javascript\ncase -1: // EOF\n  forcequirks();\n  emitDoctype();\n  emitEOF();\n  break;\n```\n\nBecause `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.\n\n### Impact & Reachability\n* **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.\n* **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.\n\n**Proof of Concept:**\n```ts\nimport { Component } from '@angular/core';\n\n@Component({\n  selector: 'app-root',\n  standalone: true,\n  template: `<div [innerHTML]=\"payload\"></div>`,\n})\nexport class AppComponent {\n  // Attacker-controlled input containing an incomplete DOCTYPE ending with whitespace\n  payload = '<!DOCTYPE html ';\n}\n```\n\n### Workarounds\n* 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.\n* Validate or sanitize user input before passing it to `[innerHTML]` on the server by stripping or rejecting strings matching `/^<!DOCTYPE/i`.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/platform-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "22.0.0"
      }, {
        "fixed" : "22.1.6"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/platform-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "21.0.0"
      }, {
        "fixed" : "21.2.23"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/platform-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "20.0.0"
      }, {
        "fixed" : "20.3.31"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/platform-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "19.2.25"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular/security/advisories/GHSA-f67j-2jqw-jpq7"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/angular/angular"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-835" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-28T21:31:21Z",
    "nvd_published_at" : null
  }
}