Threats Tagged 'cve-2026-100646'

SiYuan versions up to and including 3.8.3 contain a vulnerability in the kernel's authentication guards that fail open when the HTTP Origin header is missing. This allows cross-site GET requests from attacker-controlled pages to gain administrator privileges due to incorrect assumptions about the presence of the Origin header. The vulnerability also involves content-type sniffing on an API endpoint, enabling remote attackers to execute arbitrary scripts within the SiYuan origin and exfiltrate persistent API tokens. The issue is fixed in version 3.8.4.

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.