MCP Kotlin SDK's unbounded line buffer in StdioServerTransport/StdioClientTransport leads to memory exhaustion (DoS)
Summary
| CVE | CVE-2026-53937 |
|---|---|
| State | PUBLISHED |
| Assigner | GitHub_M |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-09-09 00:17:31 UTC |
| Updated | 2026-09-10 19:57:48 UTC |
| 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. |
Risk And Classification
Primary CVSS: v3.1 6.2 MEDIUM from [email protected]
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS: 0.001860000 probability, percentile 0.083430000 (date 2026-09-10)
Problem Types: CWE-400 | CWE-770 | CWE-400 CWE-400: Uncontrolled Resource Consumption | CWE-770 CWE-770: Allocation of Resources Without Limits or Throttling
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 6.2 | MEDIUM | CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | CNA | DECLARED | 6.2 | MEDIUM | CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
CVSS v3.1 Breakdown
Attack Vector
LocalAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Modelcontextprotocol | Io.modelcontextprotocolkotlin-sdk | affected < 0.13.0 | Not specified |
| CNA | Modelcontextprotocol | Io.modelcontextprotocolkotlin-sdk-client | affected >= 0.7.0, < 0.13.0 | Not specified |
| CNA | Modelcontextprotocol | Io.modelcontextprotocolkotlin-sdk-core | affected < 0.13.0 | Not specified |
| CNA | Modelcontextprotocol | Io.modelcontextprotocolkotlin-sdk-server | affected >= 0.7.0, < 0.13.0 | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/modelcontextprotocol/kotlin-sdk/blob/6d5bac1/kotlin-sdk-core/... | [email protected] | github.com | |
| github.com/modelcontextprotocol/kotlin-sdk/security/advisories/GHSA-74gp... | [email protected] | github.com | |
| github.com/modelcontextprotocol/kotlin-sdk/releases/tag/0.13.0 | [email protected] | github.com | |
| github.com/modelcontextprotocol/kotlin-sdk/commit/6e6f80512fb8fcc9f3c031... | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.