Summary
MCP Server Kubernetes: Tool Access Control Bypass via Presentation-Layer Filtering Without Execution-Layer Enforcement
Full technical description
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.
Fixed in v3.6.0.
Root Cause
In 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.
Proof of Concept
Tested 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:
curl -s http://<HOST>:3003/mcp \
-H 'Content-Type: application/json' \
-H 'Accept: application/json, text/event-stream' \
-d '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"kubectl_delete","arguments":{"resourceType":"pod","name":"test-pod","namespace":"default"}}}'
Result: {"result":{"content":[{"type":"text","text":"pod \"test-pod\" deleted\n"}]}}
Confirmed across ALLOW_ONLY_READONLY_TOOLS=true, ALLOW_ONLY_NON_DESTRUCTIVE_TOOLS=true, and ALLOWED_TOOLS=kubectl_get.
Credit
Discovered by Francisco Rosales of Manifold Security, coordinated by Ax Sharma, Head of Research at Manifold Security.
Impact
An 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.
The 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.
Severity 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.
The 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.
The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.
CVE-2026-46519 has a CVSS score of 8.8 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.6.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
The 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.
Frequently Asked Questions
- What is CVE-2026-46519? CVE-2026-46519 is a high-severity incorrect authorization vulnerability in mcp-server-kubernetes (npm), affecting versions < 3.6.0. It is fixed in 3.6.0. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
- How severe is CVE-2026-46519? CVE-2026-46519 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of mcp-server-kubernetes are affected by CVE-2026-46519? mcp-server-kubernetes (npm) versions < 3.6.0 is affected.
- Is there a fix for CVE-2026-46519? Yes. CVE-2026-46519 is fixed in 3.6.0. Upgrade to this version or later.
- Is CVE-2026-46519 exploitable, and should I be worried? Whether CVE-2026-46519 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-46519 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-46519? Upgrade
mcp-server-kubernetesto 3.6.0 or later.