SiYuan CVE-2026-73041

Exploitation requires (1) the ability to call the setFileAnnotation endpoint and write annotation fields to a PDF - an access level reflected by PR:L, i.e. a user/account with annotation-write privileges on the SiYuan workspace, not an anonymous remote attacker; and (2) a victim who subsequently opens the maliciously annotated PDF inside SiYuan's Electron PDF renderer (the UI:P passive-interaction requirement). The technical precondition is that SiYuan's renderer retains Node.js access, which is the default for this Electron application and is what turns the stored XSS into host code execution. Limiting factors: the attacker must already hold write access to annotations, the malicious PDF must be delivered to and opened by a victim, and single-user local installs with no shared/untrusted write access substantially reduce practical exposure.

The vendor-supplied CVSS 4.0 base score is 9.4 (Critical) with vector AV:N/AC:L/AT:N/PR:L/UI:P and High impact to both the vulnerable system and subsequent systems (VC/VI/VA and SC/SI/SA all High), consistent with sandbox-escaping RCE. The realistic risk is tempered by two limiting signals in the vector itself: PR:L means the attacker must already be able to write annotations (an authenticated or otherwise privileged actor in the SiYuan workspace), and UI:P means a victim must open the malicious PDF - this is not a spray-and-pray unauthenticated internet exploit. No EPSS score, KEV entry, or POC was provided, so exploitation probability cannot be quantified from the input; the absence of a POC and KEV listing suggests no confirmed active exploitation yet. Net: a genuinely high-severity, full-compromise bug for anyone running an affected multi-user or shared SiYuan instance, but exploitation requires a foothold plus victim interaction rather than being remotely automatable - treat as high priority for exposed/shared deployments, lower urgency for single-user local installs.

An attacker with annotation-write access to a shared SiYuan instance calls setFileAnnotation to store a PDF annotation containing a script payload; the payload is written to disk unescaped. When a colleague later opens that annotated PDF in SiYuan's Electron-based viewer, the script executes with Node.js privileges and runs attacker-chosen commands on the victim's machine. No public POC is currently identified, but the low attack complexity (AC:L) makes weaponization straightforward once write access is obtained.