# CVE-2026-40107: SiYuan Affected by Zero-Click NTLM Hash Theft and Blind SSRF via Mermaid Diagram Rendering

> Attackers can steal NTLM hashes and perform blind SSRF by tricking users into opening malicious Mermaid diagrams in SiYuan.

- **Severity:** High 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Apr 2026
- **Updated:** 10 Apr 2026
- **Also known as:** GHSA-w95v-4h65-j455, GO-2026-5702

## What is CVE-2026-40107?

CVE-2026-40107 is a high-severity server-side request forgery vulnerability in B3log Siyuan, published on 9 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

SiYuan is a personal knowledge management system. Prior to 3.6.4, 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. This vulnerability is fixed in 3.6.4.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-40107?

3 open source packages ship an affected version, including github.com/siyuan-note/siyuan/kernel. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | 0.0.0-20260407035653-2f416e5253f1 |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | 0.0.0-20260407035653-2f416e5253f1 |
| `github.com/siyuan-note/siyuan/kernel` | Go | All versions | 0.0.0-20260407035653-2f416e5253f1 |

Products: B3log Siyuan.

## How do I fix CVE-2026-40107?

Upgrade github.com/siyuan-note/siyuan/kernel to 0.0.0-20260407035653-2f416e5253f1 or later.

## Is CVE-2026-40107 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40107 exists.

## Other vulnerabilities in B3log Siyuan

- [CVE-2026-32938](https://insights.sbomify.com/CVE-2026-32938/): SiYuan has an Arbitrary File Read in its Desktop Publish Service (critical 9.9)
- [CVE-2026-33669](https://insights.sbomify.com/CVE-2026-33669/): SiYuan has Arbitrary Document Reading within the Publishing Service (critical 9.8)
- [CVE-2026-33670](https://insights.sbomify.com/CVE-2026-33670/): SiYuan has directory traversal within its publishing service (critical 9.8)
- [CVE-2026-32767](https://insights.sbomify.com/CVE-2026-32767/): SiYuan: Authorization Bypass Allows Arbitrary SQL Execution via Search API (critical 9.8)
- [CVE-2024-53504](https://insights.sbomify.com/CVE-2024-53504/): SQL injection in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40107 and fix it if it is affected.

What it is: CVE-2026-40107 is a high-severity server-side request forgery vulnerability in B3log Siyuan, published on 9 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40107 exists.

Affected packages and fixed versions:
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260407035653-2f416e5253f1
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260407035653-2f416e5253f1
- github.com/siyuan-note/siyuan/kernel (Go): affected all versions; fixed in 0.0.0-20260407035653-2f416e5253f1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-40107/ (Markdown: https://insights.sbomify.com/CVE-2026-40107/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40107
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40107
- OSV: https://osv.dev/vulnerability/CVE-2026-40107

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40107/
Summaries are generated and may contain mistakes; the official description above is the record.