CVE-2026-40107Public exploitNetwork attack vector

Credential disclosure and SSRF via Mermaid images

Published Apr 9, 2026 · Updated Apr 9, 2026

SSRF in SiYuan before 3.6.4 allows remote attackers to trigger outbound requests by causing a crafted Mermaid diagram to be rendered. Mermaid runs in loose mode with HTML labels, preserves attacker-controlled image sources in SVG foreignObject content, and inserts the SVG through innerHTML without secondary sanitization. Opening an imported or shared note triggers the request; Windows sends an NTLMv2 hash over SMB, while macOS and Linux disclose the client IP over HTTP.

CVSS severity8.7
High
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in SiYuan before 3.6.4 allows remote attackers to trigger outbound requests by causing a crafted Mermaid diagram to be rendered. Mermaid runs in loose mode with HTML labels, preserves attacker-controlled image sources in SVG foreignObject content, and inserts the SVG through innerHTML without secondary sanitization. Opening an imported or shared note triggers the request; Windows sends an NTLMv2 hash over SMB, while macOS and Linux disclose the client IP over HTTP.

The record

CVE
CVE-2026-40107
Published
Apr 9, 2026
Updated
Apr 9, 2026
Vendor
SiYuan Note
Product
SiYuan
Classifications
CWE-918, T1187
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.6.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

SiYuan Note · SiYuanversion=< 3.6.4

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
8.7GitHub, Inc.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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
T1187Forced Authentication

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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