CVE-2026-100646

Vulnerability Description

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 Score

Related Weaknesses (CWE)

References

• https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743
• https://www.vulncheck.com/advisories/siyuan-before-3.8.4-authentication-bypass-v
• https://github.com/siyuan-note/siyuan/security/advisories/GHSA-2w6q-wgc8-q743