CVE-2026-100646

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.

CVSS v3 8.1 HIGH

8.1^/10

CVSS v3 : HIGH

Vector :

Exploitability : 2.8 / Impact : 5.2

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743
https://www.vulncheck.com/advisories/siyuan-before-3.8.4-authentication-bypass-via-missing-origin-header
https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743

Configurations

No configuration.

History

30 Sep 2026, 15:21

Type	Values Removed	Values Added
References	~~() https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743 -~~	() https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743 -

26 Sep 2026, 14:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-09-26 14:16

Updated : 2026-09-30 15:21

NVD link : CVE-2026-100646

Mitre link : CVE-2026-100646

CVE.ORG link : CVE-2026-100646

JSON object : View

Products Affected

No product.

CWE

CWE-346

Origin Validation Error

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