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.

Affected: Go: github.com/siyuan-note/siyuan/kernel

**CVE:** This vulnerability corresponds to [CVE-2026-72809](https://nvd.nist.gov/vuln/detail/CVE-2026-72809).

### Summary

The kernel's `CheckAuth` grants `RoleAdministrator` to any request whose `RemoteAddr` is loopback (`127.0.0.1`), for a specific set of endpoints, and these localhost bypasses sit **outside** the `accessAuthCode` gate so they apply even when an access auth code is configured. This is demonstrated live (Part A below).

Separately, the fixed-port reverse proxy (`fixedport.go`) forwards requests to the kernel over loopback and injects no authentication token, and no `SetTrustedProxies` is configured, so gin does not derive the client address from forwarding headers. By code inspection, a request forwarded through this proxy would reach the kernel with `RemoteAddr = 127.0.0.1`. **If** the fixed-port proxy is bound to a network interface (via `NetworkServe`) and forwards remote requests to the kernel this way, the localhost bypass would grant a remote unauthenticated caller admin on those endpoints. This second step is established by reading the code but was **not reproduced end-to-end**, and I'm asking the maintainer to confirm the proxy's runtime forwarding behavior (Part B below).

### Details

**Localhost-trust admin bypass (proven).** `CheckAuth` (`session.go:298-321`) contains localhost-only bypasses that key off `RemoteAddr` and grant `RoleAdministrator`. They sit outside the `accessAuthCode` gate i.e. they apply even when an access auth code is set an…