Publish GHSA-wvj2-96wp-fq3f

Author: advisory-database[bot]

advisories/github-reviewed/2026/02/GHSA-wvj2-96wp-fq3f/GHSA-wvj2-96wp-fq3f.json

@@ -0,0 +1,66 @@
+{
+  "schema_version": "1.4.0",
+  "id": "GHSA-wvj2-96wp-fq3f",
+  "modified": "2026-02-26T22:20:08Z",
+  "published": "2026-02-26T22:20:08Z",
+  "aliases": [
+    "CVE-2026-27896"
+  ],
+  "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. 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. Additionally, Go's standard library folds the Unicode characters ſ (U+017F) and K (U+212A) to their ASCII equivalents s and k, meaning fields like \"paramſ\" would match \"params\". This violated the JSON-RPC 2.0 specification, which defines exact field names.\n\n#### Impact:\n\nA malicious MCP peer may have been able to send protocol messages with non-standard field casing (e.g., \"Method\" instead of \"method\") that the SDK would silently accept. This had the potential for:\n  - **Bypassing intermediary inspection:** Proxies or policy layers that matched on exact field names may have failed to detect or filter these messages.\n  - **Cross-implementation inconsistency:** Other MCP SDKs (TypeScript, Python) use case-sensitive parsing and would reject the same messages, creating potential security-boundary confusion.\n\n####  Fix:\n\nGo's standard JSON unmarshaling was replaced with a case-sensitive decoder (github.com/segmentio/encoding) in commit 7b8d81c. Users are advised to update to v1.3.1 to resolve this issue.\n\n#### Credits:\nMCP Go SDK thanks Francesco Lacerenza (Doyensec) for reporting this issue.",
+  "severity": [
+    {
+      "type": "CVSS_V4",
+      "score": "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"
+    }
+  ],
+  "affected": [
+    {
+      "package": {
+        "ecosystem": "Go",
+        "name": "github.com/modelcontextprotocol/go-sdk"
+      },
+      "ranges": [
+        {
+          "type": "ECOSYSTEM",
+          "events": [
+            {
+              "introduced": "0"
+            },
+            {
+              "fixed": "1.3.1"
+            }
+          ]
+        }
+      ]
+    }
+  ],
+  "references": [
+    {
+      "type": "WEB",
+      "url": "https://github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-wvj2-96wp-fq3f"
+    },
+    {
+      "type": "ADVISORY",
+      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27896"
+    },
+    {
+      "type": "WEB",
+      "url": "https://github.com/modelcontextprotocol/go-sdk/commit/7b8d81c264074404abdf5aa16e2cf0c2d9c64cc0"
+    },
+    {
+      "type": "PACKAGE",
+      "url": "https://github.com/modelcontextprotocol/go-sdk"
+    }
+  ],
+  "database_specific": {
+    "cwe_ids": [
+      "CWE-178",
+      "CWE-436"
+    ],
+    "severity": "HIGH",
+    "github_reviewed": true,
+    "github_reviewed_at": "2026-02-26T22:20:08Z",
+    "nvd_published_at": "2026-02-26T01:16:25Z"
+  }
+}