SiYuan before version 3.8.5 contains an information disclosure flaw that allows users who only have publish‑mode read access to learn the backlink block IDs and reference counts of blocks that belong to password‑protected or otherwise publish‑disabled documents. By sending POST requests to the /api/block/getDocInfo or getDocsInfo endpoints with a published document ID, an attacker can retrieve the refIDs and refCount of hidden referencing blocks, effectively bypassing the confidentiality boundary that the publish mode is supposed to enforce. This weakness is cataloged as CWE‑200, indicating an unauthorized information disclosure.

The vulnerability affects the SiYuan note application from the vendor siyuan‑note:siyuan, specifically all releases prior to 3.8.5. Any installation of SiYuan that is still running a version earlier than 3.8.5 and exposes the mentioned API endpoints to external users is susceptible.

The CVSS score of 6.9 indicates a moderate severity. The EPSS score is not available, and the vulnerability is not listed in CISA’s KEV catalog, so the publicly demonstrated exploitation likelihood is currently unknown. The likely attack vector is a remote network request to the vulnerable API endpoints, which can be performed by anyone who can reach the SiYuan instance. If an attacker can observe a published document, they can gain additional metadata that may aid further attacks or privacy violations.