MCP Kotlin SDK's unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS)
Key facts
- Attack vector
- Local
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-400.
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| MLflow | io.modelcontextprotocol:kotlin-sdk | before 0.13.0 | 0.13.0 | Patch available | CNA |
| MLflow | io.modelcontextprotocol:kotlin-sdk-client | 0.7.0 to before 0.13.0 | 0.13.0 | Patch available | CNA |
| MLflow | io.modelcontextprotocol:kotlin-sdk-core | before 0.13.0 | 0.13.0 | Patch available | CNA |
| MLflow | io.modelcontextprotocol:kotlin-sdk-server | 0.7.0 to before 0.13.0 | 0.13.0 | Patch available | CNA |
- io.modelcontextprotocol:kotlin-sdk VendorMLflow Affected before 0.13.0 Fixed in 0.13.0 Patch available CNA
- io.modelcontextprotocol:kotlin-sdk-client VendorMLflow Affected 0.7.0 to before 0.13.0 Fixed in 0.13.0 Patch available CNA
- io.modelcontextprotocol:kotlin-sdk-core VendorMLflow Affected before 0.13.0 Fixed in 0.13.0 Patch available CNA
- io.modelcontextprotocol:kotlin-sdk-server VendorMLflow Affected 0.7.0 to before 0.13.0 Fixed in 0.13.0 Patch available CNA
Remediation
- Fix · CNA io.modelcontextprotocol:kotlin-sdk (modelcontextprotocol) Fixed in 0.13.0
- Fix · CNA io.modelcontextprotocol:kotlin-sdk-client (modelcontextprotocol) Fixed in 0.13.0
- Fix · CNA io.modelcontextprotocol:kotlin-sdk-core (modelcontextprotocol) Fixed in 0.13.0
- Fix · CNA io.modelcontextprotocol:kotlin-sdk-server (modelcontextprotocol) Fixed in 0.13.0
Timeline
- 2026-10-02 Threatist record created from CVE-2026-53937
References
Other 4
- https://github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp-qhv5-v493
- https://github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031cfd693ccbcf9c4aaab
- https://github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/ReadBuffer.kt
- https://github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0
More MLflow vulnerabilities
- TI-2026-46366 Server-side request forgery in mlflow KEVCVSS 3.1CRITICAL 9.3
- TI-2023-03518 Absolute Path Traversal in mlflow/mlflow CVSS 3.1CRITICAL 10.0
- TI-2023-01113 Path Traversal: '\..\filename' in mlflow/mlflow CVSS 3.1CRITICAL 9.8
- TI-2025-31759 Redis Lua Use-After-Free may lead to remote code execution CVSS 3.1CRITICAL 10.0
- TI-2026-81527 Code execution via scorer deserialization in MLflow servers CVSS 3.1CRITICAL 9.8
- TI-2025-14028 Command Injection in mlflow/mlflow CVSS 3.1CRITICAL 10.0
Sources
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences