{"id":"CVE-2026-53937","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-53937","generatedAt":"2026-10-28T04:46:21.896Z","title":"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…","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.","published":"2026-09-09T00:17:31.000Z","lastModified":"2026-09-14T13:18:40.000Z","status":"Awaiting Analysis","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"3.1","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"},"cwe":["CWE-400","CWE-770"],"affected":[],"epss":{"score":0.00186,"percentile":0.08094,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (0.19%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"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"},{"url":"https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493","source":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-53937","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}