CVE-2026-100646 SiYuan - Broken Access Control

SiYuan <= 3.8.3 contains a broken access control caused by authentication guards failing open when HTTP Origin header is absent, letting unauthenticated remote attackers execute arbitrary scripts and invoke admin APIs, exploit requires absence of Origin header in cross-site GET requests.

CVSS base score 8.1 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.19% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Broken Access Control
Impact
Remote Code Execution, Broken Access Control, Information Disclosure
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
Published
26 September 2026
Updated
15 October 2026
Weakness
CWE-346

Vendor fix

Update to version 3.8.4 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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