SiYuan CVE-2026-73607

The SiYuan API must be network-reachable from the attacker - by default SiYuan binds to localhost only, so externally-exposed instances (configured to listen on 0.0.0.0 or a public interface, common in self-hosted or multi-user deployments) are the realistic target population. The attacker must supply a valid document identifier, which may be guessable, previously disclosed, or discoverable via other application features. No authentication or session token is required. Exploitation is limited to document outline metadata (heading identifiers and structure) - full document body content is not returned by this endpoint. Default single-user local-only deployments are not reachable externally and are therefore not practically exploitable by remote attackers.

The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:L) places this at 6.9, reflecting low-complexity, unauthenticated, network-accessible exploitation with bounded confidentiality impact - only document outline/heading structure is disclosed, not full document body content. No CISA KEV listing exists and no public POC has been identified, so real-world exploitation has not been confirmed. However, the attack is trivially automatable: it requires only a direct HTTP call with a document identifier and no credentials, which raises practical risk above what the moderate score alone conveys - particularly for multi-user SiYuan deployments exposed to untrusted networks. The SC:L component of the CVSS 4.0 vector correctly captures that documents belonging to other users (beyond the immediate requester's scope) are also disclosed. EPSS data was not provided; absence of a KEV entry and low public visibility suggest opportunistic exploitation is unlikely at this time, but targeted abuse against known SiYuan deployments is low-effort.

An attacker with network access to an externally-exposed SiYuan instance sends an unauthenticated HTTP request to /api/storage/getOutlineStorage supplying a known or enumerated document identifier. The server returns the full document outline - including heading identifiers - without verifying whether the requester has any permission to view that document. No POC has been publicly identified, but the attack requires no special tooling beyond a standard HTTP client.