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    2 vulnerabilities found for io.modelcontextprotocol:kotlin-sdk-server by modelcontextprotocol

    CVE-2026-53937 (GCVE-0-2026-53937)

    Vulnerability from nvd – Published: 2026-09-08 23:21 – Updated: 2026-09-08 23:22
    VLAI
    Title
    MCP Kotlin SDK's unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS)
    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/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.
    Severity
    6.2 (Medium)
    CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
    CWE
    • CWE-400 - Uncontrolled Resource Consumption
    • CWE-770 - Allocation of Resources Without Limits or Throttling
    Assigner
    References
    Impacted products
    Show details on NVD website
    To clipboard 

    {
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "io.modelcontextprotocol:kotlin-sdk",
          "vendor": "modelcontextprotocol",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.13.0"
            }
          ]
        },
        {
          "product": "io.modelcontextprotocol:kotlin-sdk-client",
          "vendor": "modelcontextprotocol",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.7.0, \u003c 0.13.0"
            }
          ]
        },
        {
          "product": "io.modelcontextprotocol:kotlin-sdk-core",
          "vendor": "modelcontextprotocol",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.13.0"
            }
          ]
        },
        {
          "product": "io.modelcontextprotocol:kotlin-sdk-server",
          "vendor": "modelcontextprotocol",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.7.0, \u003c 0.13.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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\u003cByteArray\u003e(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\u0027s stdin is fed by an untrusted or attacker-controlled producer (for example: a host program that exec\u0027s 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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 6.2,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-400",
              "description": "CWE-400: Uncontrolled Resource Consumption",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-770",
              "description": "CWE-770: Allocation of Resources Without Limits or Throttling",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-08T23:22:04.726Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493"
        },
        {
          "name": "https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab"
        },
        {
          "name": "https://github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt"
        },
        {
          "name": "https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0"
        }
      ],
      "source": {
        "advisory": "GHSA-74gp-qhv5-v493",
        "discovery": "UNKNOWN"
      },
      "title": "MCP Kotlin SDK\u0027s unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS)"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-53937",
    "datePublished": "2026-09-08T23:21:46.554Z",
    "dateReserved": "2026-06-11T15:46:12.318Z",
    "dateUpdated": "2026-09-08T23:22:04.726Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

    CVE-2026-53937 (GCVE-0-2026-53937)

    Vulnerability from cvelistv5 – Published: 2026-09-08 23:21 – Updated: 2026-09-08 23:22
    VLAI
    Title
    MCP Kotlin SDK's unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS)
    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/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.
    Severity
    6.2 (Medium)
    CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
    CWE
    • CWE-400 - Uncontrolled Resource Consumption
    • CWE-770 - Allocation of Resources Without Limits or Throttling
    Assigner
    References
    Impacted products
    Show details on NVD website
    To clipboard 

    {
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "io.modelcontextprotocol:kotlin-sdk",
          "vendor": "modelcontextprotocol",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.13.0"
            }
          ]
        },
        {
          "product": "io.modelcontextprotocol:kotlin-sdk-client",
          "vendor": "modelcontextprotocol",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.7.0, \u003c 0.13.0"
            }
          ]
        },
        {
          "product": "io.modelcontextprotocol:kotlin-sdk-core",
          "vendor": "modelcontextprotocol",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.13.0"
            }
          ]
        },
        {
          "product": "io.modelcontextprotocol:kotlin-sdk-server",
          "vendor": "modelcontextprotocol",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.7.0, \u003c 0.13.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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\u003cByteArray\u003e(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\u0027s stdin is fed by an untrusted or attacker-controlled producer (for example: a host program that exec\u0027s 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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 6.2,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-400",
              "description": "CWE-400: Uncontrolled Resource Consumption",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-770",
              "description": "CWE-770: Allocation of Resources Without Limits or Throttling",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-08T23:22:04.726Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493"
        },
        {
          "name": "https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab"
        },
        {
          "name": "https://github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt"
        },
        {
          "name": "https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0"
        }
      ],
      "source": {
        "advisory": "GHSA-74gp-qhv5-v493",
        "discovery": "UNKNOWN"
      },
      "title": "MCP Kotlin SDK\u0027s unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS)"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-53937",
    "datePublished": "2026-09-08T23:21:46.554Z",
    "dateReserved": "2026-06-11T15:46:12.318Z",
    "dateUpdated": "2026-09-08T23:22:04.726Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}