Vulnerability in MCP Kotlin SDK (CVE-2026-53937)
Summary
Vulnerability in MCP Kotlin SDK (CVE-2026-53937). Risk of unauthorized operations or information disclosure. Exploitable via ReadBuffer.append.
Original description
The description as published by the source.
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(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.
Source: NIST National Vulnerability Database NVD
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-53937 has been found in MCP Kotlin SDK.
Attackers can target a specific entry point like ReadBuffer.append over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.2/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "MCP Kotlin SDK CVE-2026-53937" on the vendor's site.
CVE-2026-53937 (MCP Kotlin SDK) — CWE-400 / CVSS v3 6.2
Attack vector: local / unauthenticated / no user interaction
Attack surface: ReadBuffer.append / kotlinx.io.Buffer / StdioServerTransport / StdioClientTransport
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-400) exists in MCP Kotlin SDK. Attackers reach the vulnerable code path via ReadBuffer.append without authentication.
Check the vendor advisory for the affected versions of MCP Kotlin SDK. Attack surface: ReadBuffer.append / kotlinx.io.Buffer / StdioServerTransport / StdioClientTransport.
Severity: Medium (CVSS 6.2/10). Risk of unauthorized operations or information disclosure.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで MCP Kotlin SDK を使っているサービスとバージョンを洗い出す。
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2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。