CVE-2026-27896

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Source
https://cve.org/CVERecord?id=CVE-2026-27896
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-27896.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-27896
Aliases
Downstream
Related
Published
2026-02-26T00:47:46.967Z
Modified
2026-03-02T02:47:25.893880Z
Severity
  • 7.0 (High) CVSS_V4 - CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N CVSS Calculator
Summary
MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity
Details

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.

Database specific 
{
    "cna_assigner": "GitHub_M",
    "cwe_ids": [
        "CWE-178",
        "CWE-436"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27896.json"
}
References

Affected packages

Git / github.com/modelcontextprotocol/go-sdk

Affected ranges

Type
GIT
Repo
https://github.com/modelcontextprotocol/go-sdk
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0

Affected versions

v0.*
v0.1.0
v0.2.0
v0.3.0
v0.3.1
v0.4.0
v0.5.0
v0.6.0
v0.7.0
v0.8.0
v1.*
v1.0.0
v1.1.0
v1.1.0-pre.1
v1.1.0-pre.2
v1.2.0
v1.2.0-pre.1
v1.2.0-pre.2
v1.3.0
v1.3.0-pre.1

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-27896.json"