How severe is CVE-2026-40107?

CVE-2026-40107 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2026-40107 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (22nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-40107?

CVE-2026-40107 affects B3log Siyuan. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-40107?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-40107 have an EU (EUVD) identifier?

Yes. CVE-2026-40107 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-21148.

When was CVE-2026-40107 published?

CVE-2026-40107 was published on 2026-04-09 and last updated on 2026-06-17.

CVE-2026-40107

CVE-2026-40107 is a medium-severity vulnerability in B3log Siyuan with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-918.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
CVSS v4: 8.7
EPSS exploit prediction: 0% (22nd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-21148
Weakness: CWE-918
Affected product: B3log Siyuan
Published: 2026-04-09
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-40107?: 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.
How severe is CVE-2026-40107?: CVE-2026-40107 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2026-40107 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (22nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-40107?: CVE-2026-40107 affects B3log Siyuan. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-40107?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-40107 have an EU (EUVD) identifier?: Yes. CVE-2026-40107 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-21148.
When was CVE-2026-40107 published?: CVE-2026-40107 was published on 2026-04-09 and last updated on 2026-06-17.

References

https://github.com/siyuan-note/siyuan/security/advisories/GHSA-w95v-4h65-j455

Affected products (1)

cpe:2.3:a:b3log:siyuan:*:*:*:*:*:*:*:*

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