SiYuan Affected by Zero-Click NTLM Hash Theft and Blind SSRF via Mermaid Diagram Rendering

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · 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 · score source

EPSS

• CVE-2026-40107: 0.31% estimated exploitation activity in the next 30 days; percentile 23.49 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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. On 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. Root Cause Mermaid initialization at app/src/protyle/render/mermaidRender.ts lines 28 and 33: mermaid.initialize({ securityLevel: "loose", flowchart: { htmlLabels: true, }, }); SVG injection at line 101: renderElement.lastElementChild.innerHTML = mermaidData.svg; No DOMPurify or other sanitization between the Mermaid output and DOM insertion. Mermaid v11.12.0 in "loose" mode strips active JavaScript (<script,…

Published by the source

10 Apr 2026, 19:21 UTC

Last modified by the source

10 Apr 2026, 19:21 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-w95v-4h65-j455

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# Patch Next advisory brief: CVE-2026-40107

Advisory: SiYuan Affected by Zero-Click NTLM Hash Theft and Blind SSRF via Mermaid Diagram Rendering
IDs: CVE-2026-40107, GHSA-w95v-4h65-j455
Record: https://patchnext.com/advisories/cve-2026-40107 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/siyuan-note/siyuan/kernel 0.0.0-20260407035653-2f416e5253f1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/siyuan-note/siyuan/kernel: affected < 0.0.0-20260407035653-2f416e5253f1; fixed in 0.0.0-20260407035653-2f416e5253f1

## Suggested inspection (read-only)
- Go github.com/siyuan-note/siyuan/kernel: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/siyuan-note/siyuan/kernel.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w95v-4h65-j455 (GitHub-reviewed advisory GHSA-w95v-4h65-j455 lists affected ranges: Go github.com/siyuan-note/siyuan/kernel >=0 <0.0.0-20260407035653-2f416e5253f1)

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