SiYuan EUVD-2026-39122

Exploitation requires the target SiYuan instance to be running in publish mode - the anonymous read-only HTTP endpoint served by default on port 6808 - and that port to be reachable by the attacker. No authentication, user interaction, or special privileges are needed (PR:N/UI:N), and the attack is a single double-URL-encoded request against the /assets/*path route. The limiting factors are configuration and exposure: instances not using publish mode, or with port 6808 firewalled from untrusted networks, are not exploitable by an unauthenticated remote attacker. Only versions prior to 3.7.0 are affected.

The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N, base 7.5) accurately reflects a network-reachable, low-complexity, unauthenticated read of high-value data with no integrity or availability impact - consistent with the description. Real-world priority is elevated by publicly available exploit code and by the sensitivity of the exposed files: leaking the conf/conf.json AccessAuthCode hash, API token, and sync keys can enable offline cracking or direct authenticated access, effectively turning a confidentiality-only flaw into a stepping stone toward fuller compromise. The mitigating factor is exposure scope: only instances running in publish mode (the anonymous port-6808 endpoint) are reachable by an unauthenticated attacker, so deployments not using publish mode or not exposing 6808 to untrusted networks face materially lower risk. EPSS and CISA KEV status were not provided in the input; absence of KEV data means active exploitation is not confirmed, and the public POC indicates capability but not necessarily widespread in-the-wild use.

An attacker locates an internet-exposed SiYuan instance running in publish mode on port 6808 and issues a single crafted HTTP GET to the /assets/ route with double-URL-encoded '..' segments to traverse out of the assets directory. They retrieve conf/conf.json to harvest the AccessAuthCode SHA256 hash, API token, and sync keys, then use those credentials and the leaked databases to escalate access. Publicly available exploit code lowers the skill barrier to a simple, repeatable request.