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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
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 | 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 include B3log Siyuan.
How do I fix CVE-2026-40107?
Upgrade github.com/siyuan-note/siyuan/kernel to 0.0.0-20260407035653-2f416e5253f1 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
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 SiYuan has an Arbitrary File Read in its Desktop Publish Service
- CVE-2026-33669 SiYuan has Arbitrary Document Reading within the Publishing Service
- CVE-2026-33670 SiYuan has directory traversal within its publishing service
- CVE-2026-32767 SiYuan: Authorization Bypass Allows Arbitrary SQL Execution via Search API
- CVE-2024-53504 SQL injection in n/a
Sources
Also known as GHSA-w95v-4h65-j455, GO-2026-5702.