CVE-2026-27896 | BDVDB-2026-317543 Detail
modelcontextprotocolgo-sdk
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.
Impact#
Per CVSS v3.1: confidentiality impact low, integrity impact low, availability impact none. Attack vector: network.
Weaknesses#
References#
- https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f
- https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0
- https://access.redhat.com/security/cve/CVE-2026-27896
- https://bugzilla.redhat.com/show_bug.cgi?id=2442903
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27896.json
Exploit#
No public exploit known
History#
- Version 1Record published in the CVE List.
- Version 2Most recent update recorded in the CVE List.