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TI-2026-22240 Aliases CVE-2026-27896GHSA-wvj2-96wp-fq3f

MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity

Priority LOW 37CWE-178Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
—
Confidentiality · integrity · availability
None · None · None
Fix status
Partial Red Hat: 4 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00292 21st percentileScored 2026-11-07
Fix Partial go-sdk (modelcontextprotocol): 1.3.1github.com/modelcontextprotocol/go-sdk (Go): 1.3.1Red Hat: 4 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MLflowgo-sdkbefore 1.3.11.3.1Patch availableCNA
—github.com/modelcontextprotocol/go-sdk (Go)before 1.3.11.3.1Patch availableGHSA-wvj2-96wp-fq3f
  • go-sdk VendorMLflow Affected before 1.3.1 Fixed in 1.3.1 Patch available CNA
  • github.com/modelcontextprotocol/go-sdk (Go) Vendor— Affected before 1.3.1 Fixed in 1.3.1 Patch available GHSA-wvj2-96wp-fq3f

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:lfprojects:mcp_go_sdk:*:*:*:*:*:*:*:*before 1.3.1VulnerableMLflow
  • cpe:2.3:a:lfprojects:mcp_go_sdk:*:*:*:*:*:*:*:* Versions before 1.3.1 Vulnerable ·MLflow

Remediation

  • Fix · CNA go-sdk (modelcontextprotocol) Fixed in 1.3.1
  • Fix · GHSA-wvj2-96wp-fq3f github.com/modelcontextprotocol/go-sdk (Go) Fixed in 1.3.1 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
Migration Toolkit for VirtualizationAffectedNo fix yet
OpenShift LightspeedAffectedNo fix yet
OpenShift ServerlessAffectedNo fix yet
Red Hat OpenShift AI (RHOAI)AffectedNo fix planned: Will not fix

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-27896
  2. 2026-10-03 Alias added: GHSA-wvj2-96wp-fq3f

References

Patch 2

Advisory 1

Other 1

  • TI-2026-26986 Model Context Protocol Go SDK: DNS Rebinding Protection Disabled by Default for Servers Running on Localhost CVSS 4.0HIGH 7.6
  • TI-2026-25670 MCP Go SDK Allows Cross-Site Tool Execution for HTTP Servers without Authorizatrion CVSS 3.1HIGH 7.1

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences