The vulnerability is a stored cross‑site scripting flaw in SiYuan’s Bazaar package system. The kernel renders a package README from Markdown to HTML using the lute engine with a sanitizer that blocks only legacy event attributes, allowing modern event handler attributes to slip through unchanged. The rendered HTML is injected into the main document without further sanitization or CSP headers, so an attacker can embed JavaScript that executes in the context of an administrator’s authenticated session when that administrator opens or interacts with a malicious package in the marketplace. This provides the attacker full control over the workspace, enabling arbitrary code execution, data exfiltration, or manipulation of the user’s environment.

The issue affects the SiYuan Note application (siyuan-note:siyuan) running any version earlier than 3.7.0. The fix was introduced in 3.7.0 and newer releases are not impacted.

The CVSS score of 7.1 indicates a high‑risk scenario, though there is no EPSS score available to determine current exploitation probability and the vulnerability is not listed in CISA KEV. Exploitation requires uploading or installing a malicious Bazaar package that contains a README with an event handler attribute such as onpointerover or onfocusin. Because the rendered README is inserted into the main document, the attack is achievable without a separate iframe or sandbox, and does not require the user to view external content. The likely attack path is a third‑party package author submitting malware to the Bazaar marketplace, which a privileged administrator may open and interact with, triggering the embedded script. Therefore, administrators should treat this as a high‑risk XSS that can lead to remote code execution.