{"api_version":"1","generated_at":"2026-09-11T00:21:23+00:00","cve":"CVE-2026-53937","urls":{"html":"https://cve.report/CVE-2026-53937","api":"https://cve.report/api/cve/CVE-2026-53937.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-53937","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-53937"},"summary":{"title":"MCP Kotlin SDK's unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS)","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.","state":"PUBLISHED","assigner":"GitHub_M","published_at":"2026-09-09 00:17:31","updated_at":"2026-09-10 19:57:48"},"problem_types":["CWE-400","CWE-770","CWE-400 CWE-400: Uncontrolled Resource Consumption","CWE-770 CWE-770: Allocation of Resources Without Limits or Throttling"],"metrics":[{"version":"3.1","source":"security-advisories@github.com","type":"Secondary","score":"6.2","severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","data":{"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"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"6.2","severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","data":{"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"}}],"references":[{"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/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt","refsource":"security-advisories@github.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493","name":"https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493","refsource":"security-advisories@github.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0","name":"https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0","refsource":"security-advisories@github.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab","name":"https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab","refsource":"security-advisories@github.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-53937","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-53937","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"modelcontextprotocol","product":"io.modelcontextprotocol:kotlin-sdk","version":"affected < 0.13.0","platforms":[]},{"source":"CNA","vendor":"modelcontextprotocol","product":"io.modelcontextprotocol:kotlin-sdk-client","version":"affected >= 0.7.0, < 0.13.0","platforms":[]},{"source":"CNA","vendor":"modelcontextprotocol","product":"io.modelcontextprotocol:kotlin-sdk-core","version":"affected < 0.13.0","platforms":[]},{"source":"CNA","vendor":"modelcontextprotocol","product":"io.modelcontextprotocol:kotlin-sdk-server","version":"affected >= 0.7.0, < 0.13.0","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"53937","cve":"CVE-2026-53937","epss":"0.001860000","percentile":"0.083430000","score_date":"2026-09-10","updated_at":"2026-09-11 00:05:15"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"product":"io.modelcontextprotocol:kotlin-sdk","vendor":"modelcontextprotocol","versions":[{"status":"affected","version":"< 0.13.0"}]},{"product":"io.modelcontextprotocol:kotlin-sdk-client","vendor":"modelcontextprotocol","versions":[{"status":"affected","version":">= 0.7.0, < 0.13.0"}]},{"product":"io.modelcontextprotocol:kotlin-sdk-core","vendor":"modelcontextprotocol","versions":[{"status":"affected","version":"< 0.13.0"}]},{"product":"io.modelcontextprotocol:kotlin-sdk-server","vendor":"modelcontextprotocol","versions":[{"status":"affected","version":">= 0.7.0, < 0.13.0"}]}],"descriptions":[{"lang":"en","value":"MCP Kotlin SDK is the Kotlin Multiplatform software development kit for the Model Context Protocol. 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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). 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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.","Type":"Description","Title":"MCP Kotlin SDK's unbounded line buffer in StdioServerTransport/S"}]}}}