MCP Kotlin SDK through 0.15.0 Memory Exhaustion via Application.mcpWebSocket

Advisories

MCP Kotlin SDK through 0.15.0 Memory Exhaustion via Application.mcpWebSocket

severity: high
date: 10/11/2026
Affecting: kotlin-sdk <= 0.15.0
CVE: CVE-2026-108714
CWE: CWE-770 Allocation of Resources Without Limits or Throttling
CVSS: 8.7
CVSS V4 Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
References: https://hackmd.io/@haind/mcp-kotlin-sdk-websocket-frame-allocation-dos
https://github.com/modelcontextprotocol/kotlin-sdk/blob/0.15.0/kotlin-sdk-server/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/WebSocketMcpKtorServerExtensions.kt#L41-L63
https://github.com/modelcontextprotocol/kotlin-sdk/blob/0.15.0/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/WebSocketMcpTransport.kt#L60-L85
https://github.com/modelcontextprotocol/kotlin-sdk
Credit: HaiND from the Post and Telecommunication Institute of Technology
Description: MCP Kotlin SDK through 0.15.0 contains an uncontrolled memory allocation vulnerability that allows remote clients to exhaust server memory because Application.mcpWebSocket installs Ktor WebSockets without a maxFrameSize limit. Attackers can send small frame headers declaring payloads near 2 GiB over one or a few connections, forcing huge heap allocations and causing denial of service.

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