CVE-2026-123492: SiYuan before 3.8.9 Nil Pointer Dereference DoS via MCP resources/read
SiYuan before 3.8.9 contains a nil pointer dereference vulnerability in privateCacheMiddleware that allows authenticated attackers to crash the kernel by reading nonexistent MCP resources. Attackers with a valid API token can send a resources/read request in an initialized MCP session, causing a panic that terminates the kernel process and interrupts service.
Event History
Frequently Asked Questions
What access does an attacker need to trigger the denial of service?
The attacker must be authenticated with a valid API token and have an initialized MCP session. They can then send a resources/read request for a nonexistent MCP resource.
What is the operational impact of successful exploitation?
The malformed resource read causes a panic in privateCacheMiddleware that terminates the kernel process. This interrupts service until the kernel is restored.
Which deployments are affected?
SiYuan versions before 3.8.9 are affected when MCP is in use and an attacker has a valid API token. The provided information does not state whether MCP or API-token access is enabled by default.