{
  "schema_version": "1.4.0",
  "id": "GHSA-w4q6-qw23-4rg7",
  "modified": "2026-07-28T14:35:10Z",
  "published": "2026-07-28T14:35:10Z",
  "aliases": [
    "CVE-2026-47427"
  ],
  "summary": "GitHub MCP Server has Nil Pointer Dereference DoS in completion/complete Handler",
  "details": "### Summary\n\nA nil pointer dereference vulnerability in the GitHub MCP Server causes it to crash when receiving a malformed `completion/complete` request with missing or empty parameters. This allows any unauthenticated client to cause a complete denial of service.\n\n### Details\n\nThe `CompletionsHandler` function in `pkg/github/server.go:198` accesses `params.Ref` without checking if it's nil first. When a client sends a `completion/complete` request with a missing `ref` field, the handler dereferences nil and the Go runtime panics.\n\nThe crash occurs before any authentication or token validation, so even requests with fake tokens can trigger it.\n\n### PoC\n\nAfter completing the MCP initialization handshake, send either:\n\n**Empty params:**\n\n    {\"jsonrpc\":\"2.0\",\"id\":2,\"method\":\"completion/complete\",\"params\":{}}\n\n**Missing ref field:**\n\n    {\"jsonrpc\":\"2.0\",\"id\":2,\"method\":\"completion/complete\",\"params\":{\"argument\":{\"name\":\"x\",\"value\":\"y\"}}}\n\n**Result:**\n\n    panic: runtime error: invalid memory address or nil pointer dereference\n    goroutine 42 [running]:\n    github.com/github/github-mcp-server/pkg/github.NewMCPServer.CompletionsHandler.func1(...)\n        pkg/github/server.go:198 +0x24\n\n### Impact\n\nAny unauthenticated client that can send JSON-RPC messages to the server can crash it immediately. This is a complete denial of service - the panic is unrecoverable and kills the process.\n\nAutomated fuzzing with mcpsec found 108 crashes out of 925 test cases (11.7% crash rate).\n\n### Timeline\n\n- **Feb 21, 2026** - Initial report sent to opensource-security@github.com\n- **Mar 03, 2026** - Follow-up email sent, no response\n- **Mar 21, 2026** - Re-verified on v0.33.0, sent detailed report with PoC, no response\n- **Apr 06, 2026** - GHSA filed after 44 days without acknowledgment\n\n### Suggested Fix\n\n    func (s *Server) CompletionsHandler(ctx context.Context, params *mcp.CompleteParams) (*mcp.CompleteResult, error) {\n        if params == nil || params.Ref == nil {\n            return nil, fmt.Errorf(\"invalid request: missing ref parameter\")\n        }\n        // ... rest of handler\n    }",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
    }
  ],
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/github/github-mcp-server"
      },
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.1.0"
            }
          ]
        }
      ]
    }
  ],
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/github/github-mcp-server/security/advisories/GHSA-w4q6-qw23-4rg7"
    },
    {
      "type": "WEB",
      "url": "https://github.com/github/github-mcp-server/pull/2502"
    },
    {
      "type": "WEB",
      "url": "https://github.com/github/github-mcp-server/commit/c88d2ecdd3bb07f7bdd75296e3ee676febf14f58"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/github/github-mcp-server"
    },
    {
      "type": "WEB",
      "url": "https://github.com/github/github-mcp-server/releases/tag/v1.1.0"
    }
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-476"
    ],
    "severity": "HIGH",
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-28T14:35:10Z",
    "nvd_published_at": null
  }
}