CVE-2026-73048

CVE-2026-73048 lets attackers query the SiYuan API with a publicly visible annotation ID and retrieve block identifiers from documents the attacker has no permission to access. The CVSS 5.8 score is misleading: the real threat isn't the block IDs leaked, but the structural inference attack this enables. Each annotation ID functions as a pivot key across permission boundaries—an attacker chains multiple public annotation IDs to map the topology of restricted documents without ever accessing them. In SiYuan's block-based architecture, discovering that specific restricted blocks cite a particular PDF annotation reveals concrete information about intellectual structure: subject matter, relationships to source material, logical dependencies. This is reconnaissance with compounding returns, not direct exfiltration. The 3.7.4 patch adds publish-access filtering to the returned block list, which stops the most obvious pivot. However, the underlying authorization flaw persists: the endpoint authorizes based on annotation visibility, not block ownership—a category error where one permission dimension proxies for an unrelated one. Response length, timing differences, or even consistent empty-versus-populated responses can still confirm existence of restricted documents referencing specific annotations. Beyond the patched vector, audit for orphaned annotation IDs: identifiers from deleted or downgraded documents may remain valid query keys, enabling attacks without any current public page as a starting point. The annotation ID namespace likely retains historical artifacts that outlive their authorization context. Examine adjacent endpoints for similar cross-dimensional authorization patterns—where visibility of resource A implicitly grants metadata access to resource B. This vulnerability's severity lies in what it reveals about restricted knowledge structures, not what it directly exfiltrates.

Reviewed through automated stages and approved by a human before publication.