Vulnerability details
CVE-2026-27896
MCP Go SDK Vulnerable to Improper Handling of Case Sensitivity
Official 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.
CVSS scores
| Score | Version | Source | Vector |
|---|---|---|---|
| 7.0High | 4.0 | CVEProject cvelistV5 (CNA) (GitHub_M) | 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 |
| 7.2High | 3.1 | CVEProject cvelistV5 (CNA) (redhat-SADP) | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N |
Affected products
| Vendor | Product | Versions | Source |
|---|---|---|---|
| Red Hat | Migration Toolkit for Virtualization | All | CVEProject cvelistV5 (CNA) |
| Red Hat | Migration Toolkit for Virtualization | All | CVEProject cvelistV5 (CNA) |
| Red Hat | Migration Toolkit for Virtualization | All | CVEProject cvelistV5 (CNA) |
| Red Hat | Migration Toolkit for Virtualization | All | CVEProject cvelistV5 (CNA) |
| Red Hat | Migration Toolkit for Virtualization | All | CVEProject cvelistV5 (CNA) |
| Red Hat | OpenShift Lightspeed | All | CVEProject cvelistV5 (CNA) |
| Red Hat | OpenShift Serverless | All | CVEProject cvelistV5 (CNA) |
| Red Hat | OpenShift Serverless | All | CVEProject cvelistV5 (CNA) |
| Red Hat | Red Hat OpenShift AI (RHOAI) | All | CVEProject cvelistV5 (CNA) |
| Red Hat | Red Hat OpenShift AI (RHOAI) | All | CVEProject cvelistV5 (CNA) |
| Red Hat | Red Hat OpenShift AI (RHOAI) | All | CVEProject cvelistV5 (CNA) |
| modelcontextprotocol | go-sdk | < 1.3.1 | CVEProject cvelistV5 (CNA) |
References and advisories
5- https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f x_refsource_CONFIRM
- https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0 x_refsource_MISC
- https://access.redhat.com/security/cve/CVE-2026-27896 vdb-entryx_refsource_REDHAT
- https://bugzilla.redhat.com/show_bug.cgi?id=2442903 issue-trackingx_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27896.json x_sadp-csaf-vex
Details
- Published
- 2026-02-26
- Last updated
- 2026-09-16
- State
- Published
- Assigner (CNA)
- GitHub_M
Exploit prediction (EPSS)
SSVC assessment (CISA)
- Automatable
- Yes
- Exploitation
- None
- Technical impact
- Partial
Weaknesses (CWE)
- CWE-436Interpretation Conflict
- CWE-178Improper Handling of Case Sensitivity