---
id: CVE-2026-53937
title: >-
  MCP Kotlin SDK is the Kotlin Multiplatform software development kit for the
  Model Context Protocol
summary: >-
  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…
severity: medium
cvss: 6.2
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-400
  - CWE-770
vendor: modelcontextprotocol
product: 'io.modelcontextprotocol:kotlin-sdk'
affected:
  - 'io.modelcontextprotocol:kotlin-sdk < 0.13.0'
  - 'io.modelcontextprotocol:kotlin-sdk-client >= 0.7.0, < 0.13.0'
  - 'io.modelcontextprotocol:kotlin-sdk-core < 0.13.0'
  - 'io.modelcontextprotocol:kotlin-sdk-server >= 0.7.0, < 0.13.0'
published: '2026-09-09'
updated: '2026-09-14'
sourceUpdated: '2026-09-14T13:18:40.033'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-53937'
references:
  - url: >-
      https://github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt
    label: security-advisories@github.com
  - url: >-
      https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab
    label: security-advisories@github.com
  - url: 'https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0'
    label: security-advisories@github.com
  - url: >-
      https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493
    label: security-advisories@github.com
  - url: >-
      https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - cve.org
  - exploit-available
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-14T12:09:07.813016Z'
epss: 0.00186
epssPercentile: 0.07269
ingestedAt: '2026-09-09T00:15:28.923Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.