CVE-2026-88058: Angular SSR Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-j3r3-mxqp-r2p4",
  "modified" : "2026-09-28T20:39:26Z",
  "published" : "2026-09-28T20:39:26Z",
  "aliases" : [ "CVE-2026-88058" ],
  "summary" : "Angular SSR: XSS via Unescaped Processing Instruction (<?...?>) Nodes in Fallback Raw-Content Elements",
  "details" : "### Summary\nAn 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.\n\n### Technical Description\nIn 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.).\n\nDuring 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 ?>`.\n\n### Impact & Reachability\n* **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.\n* **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.\n\n### Proof of Concept (Minimal Reproduction)\n```ts\nimport { Component, ElementRef, Renderer2, inject, DOCUMENT, AfterViewInit } from '@angular/core';\n\n@Component({\n  selector: 'app-root',\n  standalone: true,\n  template: `<noscript id=\"host\"></noscript>`\n})\nexport class AppComponent implements AfterViewInit {\n  private r = inject(Renderer2);\n  private el = inject(ElementRef);\n  private doc = inject(DOCUMENT);\n\n  ngAfterViewInit() {\n    const host = this.el.nativeElement.querySelector('#host');\n    \n    // Attacker-controlled input passed as Processing Instruction data\n    const pi = this.doc.createProcessingInstruction('x', '</noscript ');\n    this.r.appendChild(host, pi);\n    \n    // Sibling markup that should remain inert inside <noscript>\n    const img = this.r.createElement('img');\n    this.r.setAttribute(img, 'src', 'x');\n    this.r.setAttribute(img, 'onerror', 'alert(\"SSR_PI_XSS\")');\n    this.r.appendChild(host, img);\n  }\n}\n```\n**Vulnerable SSR Output**:\n```html\n<noscript><?x </noscript ?><img src=\"x\" onerror=\"alert('SSR_PI_XSS')\"></noscript>\n```\n\n### Workarounds\n* 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.\n* Manually sanitize or replace `<` with `&lt;` in any untrusted data passed to processing instruction nodes on the server.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/platform-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "22.0.0"
      }, {
        "fixed" : "22.1.4"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/platform-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "21.0.0"
      }, {
        "fixed" : "21.2.22"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@angular/platform-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "20.0.0"
      }, {
        "fixed" : "20.3.30"
      } ]
    } ]
  }, {
    "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-j3r3-mxqp-r2p4"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-88058"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular/issues/70146"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular/commit/73d8bbd27cb46495426d4132975a1355b47ad915"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular/commit/89b20568dfaee1ec8e0b3bcf1872acdddd2f4fef"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular/commit/ba3bc47b20b3d12f5eb141ec9c651373ae4d15e8"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/domino/commit/04f987dc08ff3736b427f50941adf1722458528f"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/angular/angular"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular/releases/tag/v20.3.30"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular/releases/tag/v21.2.22"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/angular/angular/releases/tag/v22.1.4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-116", "CWE-79" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-28T20:39:26Z",
    "nvd_published_at" : "2026-09-10T19:17:41Z"
  }
}