CVE-2026-27896— MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity
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I. Basic Information for CVE-2026-27896
Vulnerability Information
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Vulnerability Title
MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity
Source: NVD (National Vulnerability Database)
Vulnerability Description
The Go MCP SDK used Go's standard encoding/json.Unmarshal for JSON-RPC and MCP protocol message parsing in versions prior to 1.3.1. Go's standard library performs case-insensitive matching of JSON keys to struct field tags — a field tagged json:"method" would also match "Method", "METHOD", etc. This violated the JSON-RPC 2.0 specification, which defines exact field names. A malicious MCP peer may have been able to send protocol messages with non-standard field casing that the SDK would silently accept. This had the potential for bypassing intermediary inspection and coss-implementation inconsistency. Go's standard JSON unmarshaling was replaced with a case-sensitive decoder in commit 7b8d81c. Users are advised to update to v1.3.1 to resolve this issue.
Source: NVD (National Vulnerability Database)
CVSS Information
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Type
大小写敏感处理不恰当
Source: NVD (National Vulnerability Database)
Vulnerability Title
MCP Go SDK 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
MCP Go SDK是Model Context Protocol开源的一个模型上下文协议开发工具包。 MCP Go SDK 1.3.1之前版本存在安全漏洞，该漏洞源于JSON-RPC和MCP协议消息解析时使用大小写不敏感的JSON键匹配，可能导致绕过中间检查和跨实现不一致。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| modelcontextprotocol | go-sdk | < 1.3.1 | - |
II. Public POCs for CVE-2026-27896
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|---|
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IV. Related Vulnerabilities
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