{"id":"GHSA-cr22-wjx7-2w6m","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://\u003cHOST\u003e: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.","aliases":["CVE-2026-46519"],"modified":"2026-06-12T19:30:11.497746088Z","published":"2026-05-21T20:33:46Z","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"},"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"}],"affected":[{"package":{"name":"mcp-server-kubernetes","ecosystem":"npm","purl":"pkg:npm/mcp-server-kubernetes"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"3.6.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-cr22-wjx7-2w6m/GHSA-cr22-wjx7-2w6m.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}