SiYuan CVE-2026-85579

Requires an authenticated account with at least reader-level access (PR:L) to a SiYuan instance. The attacker must know or enumerate the root ID of at least one document visible to them. The impact is conditional on a multi-user or shared-workspace deployment where documents of different visibility tiers (private, unpublished, published) participate in cross-document undo transactions recorded in the shared global undo-log stack. Single-user installations with no shared access have no practical exposure. Document contents are not disclosed - only internal root IDs and co-transaction membership leak. The endpoint is network-accessible (AV:N) with no complexity barriers once authenticated.

The CVSS 4.0 vector (PR:L, VC:L) accurately reflects a low-severity, authenticated-only disclosure. Real-world impact is bounded: document body contents are explicitly not exposed - only internal root IDs and co-transaction relationships leak. Exploitation requires an existing authenticated session with at least reader-level privileges, narrowing the threat actor pool to insiders or users of multi-author SiYuan instances. No EPSS data was provided; KEV status is negative; no public POC is available at time of analysis. Risk is primarily relevant in multi-user collaborative deployments where documents of differing visibility (private vs. published) coexist and share undo-log transactions - single-user installations face no practical risk. The combination of low-privilege authentication requirement, metadata-only disclosure, and niche deployment footprint makes this a low real-world priority despite being a legitimate authorization design flaw.

An authenticated reader on a multi-user SiYuan deployment obtains the root ID of any document they have legitimate access to, then issues POST /api/transactions/undoState requests cycling through that root ID. The endpoint responds with peekMutatedRootIDs listing internal root IDs of private or unpublished documents that were part of the same undo transaction, revealing their existence and cross-document relationships to an actor who should have no visibility into them. No exploit code is publicly available, and the scenario requires an existing authenticated session.