SiYuan Note up to 3.8.3 Session Origin Validation kernel/model/session.go CheckAuth improper authorization

Summaryinfo

A vulnerability marked as critical has been reported in SiYuan Note SiYuan up to 3.8.3. Affected is the function CheckAuth of the file kernel/model/session.go of the component Session Origin Validation. Performing a manipulation of the argument Origin results in improper authorization. This vulnerability was named CVE-2026-100646. The attack may be initiated remotely. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in SiYuan Note SiYuan up to 3.8.3. This affects the function CheckAuth of the file kernel/model/session.go of the component Session Origin Validation. The manipulation of the argument Origin with an unknown input leads to a improper authorization vulnerability. CWE is classifying the issue as CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

SiYuan is a self-hosted personal knowledge management system. In versions up to and including 3.8.3, the kernel's authentication guards (CheckAuth in kernel/model/session.go and IsSessionOriginAllowed in kernel/util/net.go) fail open when the HTTP Origin header is absent, on the incorrect assumption that any browser-initiated cross-site request carries an Origin. Because browsers omit Origin on cross-site top-level GET navigations and no-cors GET subresource loads — and the session cookie is SameSite=Lax — a single cross-site GET issued from any attacker-controlled web page is granted RoleAdministrator, both on default installations with no access-authorization code and on password-protected instances with a live session. Combined with content-type sniffing on the /api/network/proxy endpoint, which allows attacker-controlled HTML to be served under SiYuan's own origin, this permits an unauthenticated remote attacker to execute arbitrary script in the SiYuan origin (http://127.0.0.1:6806), invoke administrator APIs, and exfiltrate the persistent kernel API token. This issue is fixed in version 3.8.4.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-100646 since 09/26/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1548.002 for this issue.

Upgrading to version 3.8.4 eliminates this vulnerability.

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Productinfo

Vendor

• SiYuan Note

Name

• SiYuan

Version

• 3.8.0
• 3.8.1
• 3.8.2
• 3.8.3

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