SiYuan versions older than 3.5.4 suffer a stored Cross‑Site Scripting flaw that allows an attacker to inject arbitrary HTML attributes into the icon field of a block via the /api/attr/setBlockAttrs endpoint. The injected payload is later rendered by the dynamic icon feature without sanitization, delivering stored XSS that, in the desktop client, can be leveraged for remote code execution. The weakness aligns with CWE‑79 for XSS and CWE‑94 for code injection.

The vulnerability affects the SiYuan personal knowledge management application (siyuan-note:siyuan). All releases prior to 3.5.4 are impacted; version 3.5.4 and later contain a fixed implementation.

The CVSS score of 5.8 reflects moderate severity, while the EPSS score under 1 % indicates a low probability of immediate exploitation and the issue is not listed in the CISA KEV catalog. An attacker would need the ability to invoke the /api/attr/setBlockAttrs API to supply a malicious icon value, typically implying authenticated access to a user’s document. Once the payload is stored it is executed whenever that block’s icon is rendered, providing a persistent XSS vector that can evolve into RCE on the desktop platform.