Vulnerability-Lookup

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

Vulnerability from cvelistv5 – Published: 2026-09-08 23:21 – Updated: 2026-09-08 23:22

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

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/modelcontextprotocol/kotlin-sd…	x_refsource_CONFIRM
https://github.com/modelcontextprotocol/kotlin-sd…	x_refsource_MISC
https://github.com/modelcontextprotocol/kotlin-sd…	x_refsource_MISC
https://github.com/modelcontextprotocol/kotlin-sd…	x_refsource_MISC

Impacted products

4 products

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

Show details on NVD website

JSON

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",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-53937",
      "date": "2026-09-09",
      "epss": "0.00186",
      "percentile": "0.08357"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-53937\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-09-09T00:17:31.407\",\"lastModified\":\"2026-09-09T00:17:31.407\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"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.\"}],\"affected\":[{\"source\":\"security-advisories@github.com\",\"affectedData\":[{\"vendor\":\"modelcontextprotocol\",\"product\":\"io.modelcontextprotocol:kotlin-sdk\",\"versions\":[{\"version\":\"\u003c 0.13.0\",\"status\":\"affected\"}]},{\"vendor\":\"modelcontextprotocol\",\"product\":\"io.modelcontextprotocol:kotlin-sdk-client\",\"versions\":[{\"version\":\"\u003e= 0.7.0, \u003c 0.13.0\",\"status\":\"affected\"}]},{\"vendor\":\"modelcontextprotocol\",\"product\":\"io.modelcontextprotocol:kotlin-sdk-core\",\"versions\":[{\"version\":\"\u003c 0.13.0\",\"status\":\"affected\"}]},{\"vendor\":\"modelcontextprotocol\",\"product\":\"io.modelcontextprotocol:kotlin-sdk-server\",\"versions\":[{\"version\":\"\u003e= 0.7.0, \u003c 0.13.0\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":6.2,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":2.5,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"security-advisories@github.com\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-400\"},{\"lang\":\"en\",\"value\":\"CWE-770\"}]}],\"references\":[{\"url\":\"https://github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0\",\"source\":\"security-advisories@github.com\"},{\"url\":\"https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493\",\"source\":\"security-advisories@github.com\"}]}}"
  }
}

FKIE_CVE-2026-53937

Vulnerability from fkie_nvd - Published: 2026-09-09 00:17 - Updated: 2026-09-09 00:17

Severity

6.2 (Medium) - CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt
	security-advisories@github.com	https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab
	security-advisories@github.com	https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0
	security-advisories@github.com	https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "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"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "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."
    }
  ],
  "id": "CVE-2026-53937",
  "lastModified": "2026-09-09T00:17:31.407",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "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"
        },
        "exploitabilityScore": 2.5,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-09-09T00:17:31.407",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-400"
        },
        {
          "lang": "en",
          "value": "CWE-770"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

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

FKIE_CVE-2026-53937

Tags

Sightings

Nomenclature