CVE-2026-50551: Stored XSS-to-RCE Chain in SiYuan Kernel Attribute View Asset Cells

What's the Vulnerability?

CVE-2026-50551 is a stored Cross-Site Scripting flaw (CWE-79, CVSS 9.9) in SiYuan's kernel (github.com/siyuan-note/siyuan/kernel). The root cause is unsanitized content in attribute view (database) asset cell fields: an attacker can inject malicious script or HTML that later executes in the context of the SiYuan kernel's rendering surface. On its own this is a stored XSS bug, but SiYuan exposes a local kernel HTTP API and plugin/asset execution surfaces that a script running in the kernel's rendering context can reach. Chaining the injection with those surfaces escalates the issue from client-side script execution to full remote code execution on the host running the SiYuan kernel service.

Affected Software

• Vendor/Project: SiYuan (go module github.com/siyuan-note/siyuan/kernel)
• Affected versions: all versions prior to 0.0.0-20260628153353-2d5d72223df4
• Patch status: no formal patch date is currently recorded; upgrade to the fixed commit/build referenced above

Exploitation Status

This vulnerability was disclosed on 2026-07-10 and a public proof-of-concept is available (poc-public). It has not been confirmed as actively exploited in the wild or added to a known-exploited-vulnerabilities catalog, but with a public PoC and a CVSS score of 9.9, defenders should treat this as a near-term, opportunistic threat rather than a theoretical one — public PoCs typically shorten the window before mass scanning and automated exploitation begin.

How Our Detection Catches It

Coverage ships across Microsoft Sentinel (KQL), Splunk (SPL), Elastic (EQL), QRadar (AQL), Sumo Logic, Chronicle (YARA-L), and CrowdStrike (CQL). The detection logic focuses on three complementary signals:

• Payload ingress: suspicious script/HTML payloads written into attribute view asset cell fields, indicating an attempted stored XSS injection.
• API abuse: anomalous calls to the SiYuan kernel's local HTTP API that are consistent with an XSS payload pivoting into the plugin/asset execution surfaces used to achieve RCE.
• Post-exploitation activity: unusual process and file-system activity on hosts running the SiYuan kernel service, catching the RCE stage even if the initial injection was missed.

Layering these three stages gives coverage across the full attack chain, from initial stored payload to code execution on the host.

Full Detection Details

For the complete KQL, SPL, and other SIEM queries along with MITRE ATT&CK mapping, see the CVE-2026-50551 detection page.