SiYuan EUVD-2026-39124

Exploitation requires two concrete conditions: (1) the attacker must have network reachability to SiYuan's HTTP API port - the description characterizes this as network-adjacent, meaning the same LAN segment or a SiYuan instance that has been bound to a non-loopback interface; and (2) the attacker must supply a valid SiYuan block ID in the request parameter. Block IDs in SiYuan follow a timestamp-derived format, which may reduce the entropy of guessing or allow enumeration. No authentication, session token, or user interaction is required - the endpoint is explicitly exempted from SiYuan's auth middleware. Exploitation is limited by: block ID availability (a soft but not hard prerequisite), network proximity (default localhost binding limits exposure), and the read-only nature of the SQL access (no write or code execution path via this endpoint). The type=8 parameter specifically must be used to trigger the vulnerable template rendering path.

The provided CVSS 3.1 score of 5.9 (AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N) captures the core trade-off: the confidentiality impact is high (full database read), but exploitation complexity is elevated because a valid block ID must be known in advance. There is a notable discrepancy between the CVSS attack vector (AV:N, implying internet-reachable) and the description's characterization of the attacker as 'network-adjacent,' which better matches SiYuan's typical deployment as a locally-bound desktop or self-hosted personal tool. AV:A is likely the more accurate metric; if SiYuan is not externally exposed, the practical attacker population shrinks considerably. No public exploit code, proof-of-concept, or CISA KEV listing has been identified, and EPSS data was not provided in the source intelligence. The absence of a POC reduces near-term opportunistic risk, but the block ID requirement is a soft prerequisite - block IDs follow a deterministic format and may be guessable or obtainable through other application interactions (e.g., shared links). Overall: elevated real-world risk for multi-user or network-exposed SiYuan deployments; low risk for single-user instances bound to localhost with no external exposure.

An attacker on the same local network as a SiYuan instance - or one who has obtained a valid SiYuan block ID through a shared note link or prior reconnaissance - sends a crafted unauthenticated GET request to /api/icon/getDynamicIcon?type=8&id=<blockID>. The endpoint renders a Go template invoking querySQL against the SQLite database without any credential check, and the full contents of the user's notes, tags, and metadata are returned in the response. No public proof-of-concept has been identified at time of analysis, but the attack requires no special tooling beyond a standard HTTP client.