CVE-2026-46519: MCP Server Kubernetes Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-cr22-wjx7-2w6m",
  "modified" : "2026-06-12T19:26:31Z",
  "published" : "2026-05-21T20:33:46Z",
  "aliases" : [ "CVE-2026-46519" ],
  "summary" : "MCP Server Kubernetes: Tool Access Control Bypass via Presentation-Layer Filtering Without Execution-Layer Enforcement",
  "details" : "## Summary\n\n`mcp-server-kubernetes` exposes three environment variables (`ALLOW_ONLY_READONLY_TOOLS`, `ALLOW_ONLY_NON_DESTRUCTIVE_TOOLS`, `ALLOWED_TOOLS`) documented as access controls for restricting which Kubernetes operations are available. These controls are enforced at the tool discovery layer (`tools/list`) but not at the execution layer (`tools/call`). Any client that knows a tool name can invoke it directly regardless of the configured restriction mode. The access control was effectively cosmetic.\n\nFixed in v3.6.0.\n\n## Impact\n\nAn attacker or misconfigured AI agent with network access to the MCP server's HTTP endpoint could invoke any Kubernetes tool regardless of the restriction mode configured by the operator -- including `kubectl_delete`, `exec_in_pod`, `kubectl_generic`, and `node_management`.\n\nThe project explicitly supports and documents multi-client HTTP deployment scenarios (Streamable HTTP and SSE transports, in-cluster deployments, Codex CLI and Gemini CLI integrations). In these deployments, operators relied on the tool restriction env vars to enforce least-privilege access across users or roles. The bypass invalidated that model entirely.\n\nSeverity scales with the Kubernetes service account's permissions. In environments where the MCP server runs with `cluster-admin` (common in dev/staging), this is equivalent to full cluster compromise for any client that can reach the endpoint.\n\nThe `MCP_AUTH_TOKEN` / `X-MCP-AUTH` mechanism controls who can reach the endpoint but provides no per-tool authorization. An authenticated client restricted to `ALLOWED_TOOLS=kubectl_get` could still invoke `kubectl_delete` after authentication.\n\n## Root Cause\n\nIn `src/index.ts`, the `ListToolsRequestSchema` handler applied the configured filtering logic before returning available tools. The `CallToolRequestSchema` handler dispatched directly by tool name with no equivalent check -- every tool was reachable unconditionally.\n\n## Proof of Concept\n\nTested across all three restriction modes against a live kind cluster. In each case, `kubectl_delete` was absent from `tools/list` but executed successfully via a direct `tools/call` request:\n\n```shell\ncurl -s http://<HOST>:3003/mcp \\\n  -H 'Content-Type: application/json' \\\n  -H 'Accept: application/json, text/event-stream' \\\n  -d '{\"jsonrpc\":\"2.0\",\"id\":2,\"method\":\"tools/call\",\"params\":{\"name\":\"kubectl_delete\",\"arguments\":{\"resourceType\":\"pod\",\"name\":\"test-pod\",\"namespace\":\"default\"}}}'\n```\n\nResult: `{\"result\":{\"content\":[{\"type\":\"text\",\"text\":\"pod \\\"test-pod\\\" deleted\\n\"}]}}`\n\nConfirmed across `ALLOW_ONLY_READONLY_TOOLS=true`, `ALLOW_ONLY_NON_DESTRUCTIVE_TOOLS=true`, and `ALLOWED_TOOLS=kubectl_get`.\n\n## Remediation\n\nThe fix applies the same filtering logic from `ListToolsRequestSchema` at the start of the `CallToolRequestSchema` handler, returning an error for any tool call outside the active allowed set. Fixed in v3.6.0.\n\n## Credit\n\nDiscovered by [Francisco Rosales](https://www.linkedin.com/in/francisco-rosales-celis/) of [Manifold Security](https://manifold.security), coordinated by [Ax Sharma](https://www.linkedin.com/in/axsharma/), Head of Research at Manifold Security.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "mcp-server-kubernetes"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.6.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Flux159/mcp-server-kubernetes/security/advisories/GHSA-cr22-wjx7-2w6m"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-46519"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Flux159/mcp-server-kubernetes"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Flux159/mcp-server-kubernetes/releases/tag/v3.6.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-863" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-21T20:33:46Z",
    "nvd_published_at" : "2026-06-11T19:16:42Z"
  }
}