SiYuan EUVD-2026-57410

For the primary (local) attack path: attacker must have the ability to send HTTP requests to the SiYuan kernel's loopback address on the host machine - local user access or process-level access is required, but no SiYuan credentials or OS-level elevated privileges are needed. The bypass is limited to the specific endpoint set: /api/system/exit, getNetwork, getWorkspaceInfo, /assets/*, and /export/*; it does not grant admin access across all SiYuan functionality. For the secondary (remote) attack path: the SiYuan fixed-port reverse proxy must be bound to a network-accessible (non-loopback) interface, which is a non-default or explicitly misconfigured deployment state. A critical limiting factor for defenders: enabling the SiYuan access auth code does NOT protect these endpoints, because the loopback trust check sits outside the auth code gate. The bypass is version-agnostic across all v3.7.2 and earlier releases regardless of OS platform.

The CVSS 4.0 vector (AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:H/SC:N/SI:N/SA:N, score 7.1) correctly anchors the primary exploitation path as local: an attacker with access to the host machine can trivially reach the kernel's loopback interface without any credentials. A secondary remote vector exists if the fixed-port proxy is bound to a non-loopback interface, but the advisory explicitly cautions that this path was not reproduced end-to-end - a meaningful credibility gap that should prevent treating this as a confirmed remote-exploitable flaw. No EPSS score was provided in the input data. Absence from the CISA KEV catalog and lack of any identified POC further reduce real-world urgency beyond patching. For typical SiYuan deployments running on a single workstation, the local attack vector means an adversary would already need host-level access, substantially limiting incremental risk. Risk is materially higher for users who expose the proxy port externally or run SiYuan in shared/server environments.

A local attacker with shell or network access to the SiYuan host sends an unauthenticated HTTP GET request to the kernel's loopback endpoint - for example, targeting /export/* to retrieve all notebook files or /api/system/exit to crash the application - and CheckAuth grants administrator access based solely on the 127.0.0.1 source address. If the fixed-port proxy is misconfigured to listen on a LAN or internet-facing interface, an external attacker could send an HTTP request through the proxy, which forwards it to the kernel with RemoteAddr=127.0.0.1, triggering the same bypass without any credentials. No public exploit code has been identified, and the remote path was not confirmed end-to-end by the advisory authors.