Answer in brief
CVE-2026-53937 records a Medium severity (CVSS 6.2) vulnerability in MCP Kotlin SDK's unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS). The current sources do not mark it as known exploited. The current feed maps modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk (generic), modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk-client (generic), modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk-core (generic), modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk-server (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 6.2. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk (generic), modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk-client (generic), modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk-core (generic), modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk-server (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| modelcontextprotocol/io.modelcontextprotocol:kotlin-sdkgeneric | <0.13.0 | 0.13.0 |
| modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk-clientgeneric | >=0.7.0 <0.13.0 | 0.13.0 |
| modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk-coregeneric | <0.13.0 | 0.13.0 |
| modelcontextprotocol/io.modelcontextprotocol:kotlin-sdk-servergeneric | >=0.7.0 <0.13.0 | 0.13.0 |
Published upstream
Sep 8, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 14, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Sep 8, 2026
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.
Quoted source text, attributed separately from HOL analysis.