A flaw in SiYuan prior to version 3.7.4 allows attackers to inject arbitrary markup into PDF annotation fields. When a user opens an annotated PDF, the embedded script executes inside the PDF renderer with full Node.js privileges, permitting full control over the host system. The vulnerability is a classic example of unsanitized input leading to browser‑style script execution, classified as CWE‑79.

The issue affects the SiYuan note-taking application. Any installation of the product with a version earlier than 3.7.4 is vulnerable. The vulnerability is triggered via the setFileAnnotation API endpoint, which writes annotation data directly to disk without validation or escaping.

The CVSS score of 9.4 indicates a critical severity. No EPSS information is presently available, so the likelihood of exploitation is unknown, and the vulnerability is not listed in CISA’s KEV catalog. The attack vector is inferred to be remote, requiring an attacker to deliver a malicious PDF to a user with the application installed. If opened, the PDF renderer will run the injected script with full Node.js access, providing remote attackers with the ability to execute arbitrary code on the victim’s machine.