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CVE-2026-53937— MCP Kotlin SDK's unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS)

Quick assessment

Affected
modelcontextprotocol io.modelcontextprotocol:kotlin-sdk
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

MCP Kotlin SDK 是用于模型上下文协议（Model Context Protocol, MCP）的 Kotlin 多平台软件开发工具包。在 0.7.0 至 0.12.0 版本中，位于 中的 方法会将来自 stdio 传输层接收到的每一块字节无上限地写入 。帧数据只有当检测到换行符 （0x0a）字节时才会从该缓冲区中提取。若对端持续流式发送字节但始终不发送换行符，内部缓冲区将无限增长，直至 JVM（或宿主进程）因内存溢出（OOM）被强制终止。 该内存泄漏问题在 和 中被进一步放大：二者均通过 队列接收原始

CVSS 6.2 · Medium

Possible ATT&CK Techniques 1 AI

T1029 · Scheduled Transfer
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I. Basic Information for CVE-2026-53937

Vulnerability Information
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Vulnerability Title
MCP Kotlin SDK's unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS)
Source: CVE Program / CVE List V5
Vulnerability Description
MCP Kotlin SDK is the Kotlin Multiplatform software development kit for the Model Context Protocol. In versions 0.7.0 through 0.12.0, `ReadBuffer.append` in `kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt` writes every chunk of bytes received from the stdio transport into a `kotlinx.io.Buffer` with no size cap. Frames are extracted from that buffer only when a `\n` (0x0a) byte is observed. A peer that streams bytes without ever sending a newline causes the internal buffer to grow indefinitely until the JVM (or the surrounding host process) is OOM-killed. The leak is amplified by `StdioServerTransport` and `StdioClientTransport`, which both queue raw chunks through a `kotlinx.coroutines.channels.Channel<ByteArray>(Channel.UNLIMITED)` and then call `readBuffer.append(chunk)` without backpressure or size guard. This is a remote-pre-auth denial of service whenever an SDK stdio server's stdin is fed by an untrusted or attacker-controlled producer (for example: a host program that exec's the MCP server as a subprocess and pipes through bytes received from a network peer, or a sidecar wrapper that proxies bytes from an HTTP endpoint to the stdio transport). Version 0.13.0 fixes the issue.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
modelcontextprotocol io.modelcontextprotocol:kotlin-sdk < 0.13.0 -
modelcontextprotocol io.modelcontextprotocol:kotlin-sdk-client >= 0.7.0, < 0.13.0 -
modelcontextprotocol io.modelcontextprotocol:kotlin-sdk-core < 0.13.0 -
modelcontextprotocol io.modelcontextprotocol:kotlin-sdk-server >= 0.7.0, < 0.13.0 -

II. Public POCs for CVE-2026-53937

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III. Intelligence Information for CVE-2026-53937

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Patches & Fixes for CVE-2026-53937 (2)

Vendor Advisories for CVE-2026-53937 (1)

Vendor Pages for CVE-2026-53937 (1)

IV. Related Vulnerabilities

Same vendor: modelcontextprotocol
Same weakness: CWE-400

V. Comments for CVE-2026-53937

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