Denial of Service via Uncontrolled Memory Allocation in MCP Kotlin SDK

The MCP Kotlin SDK, specifically versions up to and including 0.15.0, contains an uncontrolled memory allocation vulnerability (CVE-2026-108714) within the Application.mcpWebSocket component. The vulnerability arises because the SDK initializes Ktor WebSockets without explicitly configuring a maxFrameSize limit. This oversight allows a remote attacker to send crafted WebSocket frame headers that declare very large payload sizes, approaching 2 GiB. By initiating one or a small number of concurrent connections and sending these malformed headers, an attacker can force the server to attempt massive heap allocations, leading to rapid memory exhaustion and a subsequent denial of service (DoS) state. This vulnerability impacts any service utilizing the affected SDK version for WebSocket communication, as the resource consumption occurs before the application logic processes the data.

Impact

Successful exploitation results in an immediate denial of service for the target application. By consuming available heap memory, the attack forces the JVM to trigger excessive garbage collection cycles or causes an OutOfMemoryError, rendering the service unresponsive to legitimate users. Given the nature of WebSocket services, this disruption affects real-time communication channels and connected clients, potentially impacting broader infrastructure depending on the application's role.

Recommendation

1. Patch immediately by upgrading to a version of the MCP Kotlin SDK that enforces a mandatory maxFrameSize limit in the Application.mcpWebSocket configuration.
2. Implement global memory monitoring and alerting for JVM heap usage to detect rapid, anomalous memory spikes that precede a crash.
3. Review existing Ktor WebSocket configurations in all applications using the MCP Kotlin SDK to ensure maxFrameSize and maxFrameSize are explicitly constrained to reasonable bounds appropriate for the application traffic.