The organisation loses trust in the endpoint path that carries bearer tokens to the service. Even if the token is legitimate, the routing layer can proxy or capture it before the SaaS provider ever sees the request. That turns workstation configuration into an identity control plane with no effective boundary.
Why This Matters for Security Teams
When local MCP configuration can be rewritten by untrusted code, the workstation stops being a passive client and becomes part of the identity control plane. That matters because Model Context Protocol connectors often carry bearer tokens, API keys, and routing instructions in the same local path that code can influence. Once an attacker or compromised tool can alter that path, legitimate credentials can be redirected before the SaaS provider ever evaluates the request.
For security teams, the risk is not just credential theft. It is silent policy bypass, because the endpoint trust boundary has been collapsed into the local runtime. This is why MCP security guidance increasingly treats configuration integrity as a first-class control, not an admin convenience. The issue is also visible in broader agentic AI risk research, including The State of MCP Server Security 2025 and the OWASP view of agentic application abuse in OWASP Agentic AI Top 10.
In practice, many security teams encounter credential interception only after an MCP integration has already been used to proxy requests or exfiltrate secrets, rather than through intentional review of the local trust model.
How It Works in Practice
The core failure is that untrusted code can rewrite the local configuration used to resolve an MCP server, transform a benign endpoint into a malicious relay, or swap out a tool target while preserving a valid bearer token. The token may still be cryptographically valid, but it is now traveling through an attacker-controlled path. That means the issue is not authentication failure at the SaaS layer. It is integrity failure at the client layer.
Current guidance suggests treating MCP configuration files, launcher arguments, and environment injection as sensitive control points. The practical response is to reduce what local code can change, limit where tokens can be loaded, and separate configuration from secrets. Where possible, use short-lived credentials and task-specific scopes rather than static values that remain usable after configuration has been tampered with. This aligns with the direction of the Analysis of Claude Code Security, which shows how agentic tooling can amplify ordinary configuration weaknesses into identity exposure.
- Lock down MCP config directories so untrusted processes cannot write or replace them.
- Store secrets outside editable config files and inject them only at runtime.
- Validate the endpoint, tool name, and issuer before any token is sent.
- Use per-session or per-task credentials with narrow scope and short TTL.
- Prefer signed, centrally managed workload identity where the client proves what it is, not what it claims in a file.
These controls tend to break down when local development environments allow arbitrary scripts, plugin hooks, or auto-updaters to rewrite MCP paths because the same privileges that support rapid iteration also defeat config integrity.
Common Variations and Edge Cases
Tighter configuration control often increases developer friction, requiring organisations to balance local flexibility against endpoint trust. That tradeoff is real, especially in research, prototyping, and code-assist workflows where MCP servers are added and removed frequently.
There is no universal standard for this yet, but best practice is evolving toward a split model: untrusted local code may request access, but only a trusted runtime or policy layer can mint the final credential or approve the destination. That is the difference between “a file says this is allowed” and “the runtime verifies this request right now.” For agentic environments, the OWASP Agentic AI Top 10 and the related OWASP Top 10 for Agentic Applications 2026 both point toward runtime enforcement rather than static trust in local settings.
Edge cases matter. Shared workstations, containerised dev shells, and IDE extensions can all rewrite configuration indirectly. So can dependency install scripts and post-launch hooks. If the environment permits local code execution, then config rewrite should be assumed possible unless the filesystem, runtime policy, and secret injection path are all separately controlled.
In practice, organisations that fail here usually discover the problem when a benign-looking MCP helper has already redirected traffic, exposed tokens, or chained access into a wider agent workflow.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
OWASP Agentic AI Top 10 and CSA MAESTRO address the attack and risk surface, while NIST AI RMF set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| OWASP Agentic AI Top 10 | A01 | Covers agent/tool abuse when local config rewrites redirect token-bearing requests. |
| CSA MAESTRO | T2 | Addresses agentic trust boundaries and runtime authorization for tool use. |
| NIST AI RMF | GOVERN | Governance requires accountability for identity-path changes made by untrusted code. |
Assign ownership for MCP config integrity and review how identity flow changes are approved and monitored.
Related resources from NHI Mgmt Group
- What are the risks of using static credentials in MCP servers?
- What breaks when hardcoded credentials are left in code or configuration files?
- What breaks when a workflow engine can execute untrusted code inside the same environment that stores secrets?
- What breaks when Claude Code hooks are left as local developer settings?
