SiYuan Note up to 3.7.3 Kernel CheckAuth improper authentication

Summaryinfo

A vulnerability, which was classified as critical, has been found in SiYuan Note SiYuan up to 3.7.3. Affected is the function CheckAuth of the component Kernel. The manipulation leads to improper authentication. This vulnerability is documented as CVE-2026-72809. The attack can be initiated remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in SiYuan Note SiYuan up to 3.7.3 and classified as critical. This issue affects the function CheckAuth of the component Kernel. The manipulation with an unknown input leads to a improper authentication vulnerability. Using CWE to declare the problem leads to CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

SiYuan versions <= v3.7.2 (patched in v3.7.4) contain an authentication bypass vulnerability in the kernel's CheckAuth function, which grants the administrator role (RoleAdministrator) to any request whose RemoteAddr is loopback (127.0.0.1) for a specific set of endpoints (including /api/system/exit, getNetwork, getWorkspaceInfo, /assets/*, and /export/*). These localhost bypasses sit outside the access auth code gate, so they apply even when an access auth code is configured. Because the fixed-port reverse proxy forwards requests to the kernel over loopback without injecting an authentication token and does not configure trusted proxies, a request forwarded through this proxy reaches the kernel with RemoteAddr = 127.0.0.1. If the fixed-port proxy is bound to a network interface, this could allow a remote unauthenticated attacker to obtain admin access on the affected endpoints; however, per the advisory this remote forwarding behavior was established only by code inspection and was not reproduced end-to-end.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-72809 since 08/10/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available.

Upgrading to version 3.7.4 eliminates this vulnerability.

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Productinfo

Vendor

• SiYuan Note

Name

• SiYuan

Version

• 3.7.0
• 3.7.1
• 3.7.2
• 3.7.3

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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