CVE-2026-27896
Essential information
- Published
- 26/02/2026 01:16
- Modified
- 27/02/2026 14:06
- Author
- —
- Creator
- —
- CVSS
- 7.0 HIGH (v3) 7.0 HIGH (v4.0)
- CISA KEV
- No
- CWE
- —
- CVSS vector
-
—
—
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS metrics
- Access vector
- —
- Access complexity
- —
- Authentication
- —
- Confidentiality impact
- —
- Integrity impact
- —
- Availability impact
- —
- Exploitability
- —
- Remediation level
- —
- Report confidence
- —
- Temporal score
- —
- Attack vector
- —
- Attack complexity
- —
- Privileges required
- —
- User interaction
- —
- Scope
- —
- Confidentiality impact
- —
- Integrity impact
- —
- Availability impact
- —
- Exploit code maturity
- —
- Remediation level
- —
- Report confidence
- —
- Temporal score
- —
- Attack vector
- NETWORK
- Attack complexity
- LOW
- Attack requirements
- PRESENT
- Privileges required
- NONE
- User interaction
- NONE
- Confidentiality (V)
- NONE
- Confidentiality (S)
- HIGH
- Integrity (V)
- NONE
- Integrity (S)
- HIGH
- Availability (V)
- NONE
- Availability (S)
- NONE
- Exploit maturity
- NOT_DEFINED
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.
NVD status
- Status
- Awaiting Analysis — CVE has been recently published to the CVE List and has been received by the NVD.
- Source
- [email protected]
- NVD
- View on NVD
Affected products (CPE)
| Product | CPE |
|---|---|
| go / mcp sdk | cpe:2.3:a:go:mcp_sdk:<1.3.1:*:*:*:*:*:*:* |