SiYuan CVE-2026-74802

Exploitation requires the victim to have SiYuan running locally with its kernel reachable on the default port (typically localhost:6806) and to visit an attacker-controlled webpage in a browser on the same host during that session. No SiYuan authentication is required of the attacker - the cross-origin WebSocket connection bypasses SiYuan's admin-only intent by exploiting the missing origin check before any session validation. Exploitation is bounded by: (1) SiYuan must be actively running at the time of the visit; (2) the victim's browser must be on the same host as the SiYuan kernel; (3) the target endpoint must be network-reachable from the victim's machine for the pivoting impact to be realized. It is not remotely exploitable against hosts where the victim is not actively running SiYuan.

The real-world risk is moderate and context-dependent. The CVSS 4.0 score of 7.1 reflects meaningful confidentiality and integrity impact (VC:H, VI:L), but several signals temper urgency: EPSS is 0.10% at the 1st percentile, indicating very low observed exploitation probability across the broader threat landscape. SSVC rates exploitation as 'poc' (not active), automatable as 'no', and technical impact as 'partial' - a profile consistent with a demonstrated-but-not-weaponized issue. The attack requires the victim to simultaneously be running SiYuan and browse to an attacker-controlled page, which limits opportunistic exploitation. The primary consequence - network pivoting to internal hosts - is significant in environments where SiYuan users have access to sensitive internal network segments, but SiYuan is niche personal software and most deployments will be on developer or researcher workstations rather than high-value infrastructure. No conflicting signals between data sources were identified; CVSS vector (UI:P/PR:N) and description are consistent.

A victim running SiYuan locally visits a malicious webpage in their browser while SiYuan's kernel is active on localhost:6806. The page executes JavaScript that opens a WebSocket to ws://localhost:6806/ws/network/proxy - SiYuan accepts the cross-origin connection due to the disabled origin check - and the attacker's script then issues proxy commands directing the SiYuan kernel to relay requests to internal network targets such as private IP ranges or cloud metadata services (e.g., 169.254.169.254), enabling reconnaissance and data exfiltration through the victim's machine. SSVC confirms a POC exists, making this scenario operationally feasible for a motivated attacker.