CVE-2026-74798 is a path traversal vulnerability in the SiYuan kernel prior to version 3.7.4, specifically in the database_clean MCP tool. The tool insufficiently validates the id parameter, performing only an empty-string check before passing it to RemoveUnusedAttributeView, which constructs filesystem paths without verifying that id conforms to the expected node-ID format. An authenticated MCP client can exploit this by supplying path traversal sequences in id, causing the kernel to copy arbitrary readable files into SiYuan's history directory and subsequently delete the original files. While the HTTP API handler was secured in a separate advisory (GHSA-7hm9-v7vf-7g4w), the MCP interface remains vulnerable. The vulnerability has a CVSS 4.0 score of 9.3, indicating critical severity. No patch or official remediation level has been published to date.

An authenticated MCP client can exploit this vulnerability to read arbitrary files accessible by the SiYuan process and delete those files from the filesystem. This can lead to unauthorized data disclosure and data loss. The vulnerability affects the integrity and confidentiality of the system running the SiYuan kernel prior to version 3.7.4.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since the HTTP API handler was hardened but the MCP caller remains vulnerable, avoid using the MCP interface until an official fix is released. Monitor vendor communications for updates and apply patches promptly once available.