SiYuan EUVD-2026-52275

Exploitation requires that the SiYuan instance is running with the publish feature reachable over the network and that the target content exists as publish-disabled documents on that same instance; the attacker must obtain a valid heading block ID for the restricted content and call one of getHeadingDeleteTransaction, getHeadingLevelTransaction, or getHeadingInsertTransaction. Per CVSS AV:N/AC:L/PR:N/UI:N, no authentication or user interaction is needed once the publish endpoint is reachable. Limiting factors: instances that do not use publish mode, or that keep the publish interface off the network / behind additional authentication, are not exposed; the attacker also needs a way to know or enumerate valid heading block IDs, and impact is confidentiality-only (no modification or denial of service).

The supplied CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/SC:H) and 9.2 score describe network-reachable, unauthenticated, low-complexity access with high confidentiality impact and no integrity or availability impact - consistent with the description of anonymous read access to restricted rendered content. Confidence in the technical claim is high (VulnCheck research plus a vendor GHSA advisory), but real-world urgency is moderated by missing signals: no EPSS score was provided, there is no SSVC decision record in the input, the CVE is not in CISA KEV, and no public POC is identified, so this is not confirmed as actively exploited. The 9.2 rating is driven largely by the unauthenticated confidentiality-only impact; practical severity depends on whether an instance actually runs publish mode with sensitive publish-disabled documents - a purely local/private SiYuan install with publishing disabled is not exposed. Net: a genuine, easy-to-exploit confidentiality bug for internet-exposed publish deployments, but likely targeted rather than mass-exploited given the niche product footprint.

An attacker who can reach a SiYuan instance's publish interface as an anonymous reader (or with a RoleReader token) enumerates or guesses a heading block ID belonging to a publish-disabled document and calls getHeadingInsertTransaction (or the delete/level variants). The endpoint returns the rendered block DOM of that restricted content, leaking notes the owner never intended to publish. No authentication, user interaction, or high attack complexity is required per the CVSS vector; no public POC is currently identified.