AI agents use set_global_header to create or update resources in Mitmproxy — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mitmproxy environment.
The tool modifies HTTP headers globally across intercepted traffic, which is a reversible write operation. However, severity is high because setting headers globally can affect authentication, CORS, security headers, and session handling across all traffic, potentially breaking applications or enabling injection attacks.
From the tool's definition Tool name 'set_global_header' and server context 'modify...HTTP/HTTPS traffic in real-time' indicate modification of request/response headers. Empty description limits precision.
Documented attack patterns abuse exactly the kind of access set_global_header gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Mitmproxy, and nothing reaches the server without passing your rules. This is the rule we recommend for set_global_header:
{
"version": "1",
"default": "deny",
"tools": {
"set_global_header": {
"limits": [
{
"counter": "set_global_header_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_global_header stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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set_global_header. It is categorised as a Write tool in the Mitmproxy MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mitmproxy MCP server in PolicyLayer and add a rule for set_global_header: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Mitmproxy. Nothing to install.
set_global_header is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the set_global_header rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for set_global_header. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
set_global_header is provided by the Mitmproxy MCP server (snapspecter/mitmproxy-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 25 Mitmproxy tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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25 Mitmproxy tools catalogued and risk-classified — across an index of 42,500+ MCP servers.