{"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":0.08474,"ingestedAt":"2026-09-09T00:15:28.923Z","slug":"CVE-2026-53937","body":"## Overview\n\nMCP 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":46,"depthScoreParts":{"impact":34.1,"likelihood":0,"exploitation":12,"ransomware":0},"changes":[{"seq":201762,"id":"CVE-2026-53937","ts":1789399675251,"field":"exploit_available","old":"false","new":"true"},{"seq":200492,"id":"CVE-2026-53937","ts":1789397340390,"field":"exploit_available","old":"true","new":"false"},{"seq":198409,"id":"CVE-2026-53937","ts":1789391901834,"field":"exploit_available","old":"false","new":"true"}]}