From bafd5419fabbd30415c3b782e778ba971f8019e7 Mon Sep 17 00:00:00 2001
From: Jeremiah Lowin <153965+jlowin@users.noreply.github.com>
Date: Sat, 7 Mar 2026 12:10:05 -0500
Subject: [PATCH] Redact sensitive headers in OpenAPI provider debug logging
 (#3436)

* Redact sensitive headers in OpenAPI provider debug logging (#3427)

* Use safe-header allowlist instead of sensitive-header denylist for redaction
---
 .../server/providers/openapi/components.py    | 23 ++++++++-
 .../openapi/test_openapi_features.py          | 47 ++++++++++++++++++-
 2 files changed, 68 insertions(+), 2 deletions(-)

diff --git a/src/fastmcp/server/providers/openapi/components.py b/src/fastmcp/server/providers/openapi/components.py
index 1f52033fa..7d7722666 100644
--- a/src/fastmcp/server/providers/openapi/components.py
+++ b/src/fastmcp/server/providers/openapi/components.py
@@ -29,6 +29,25 @@ from fastmcp.utilities.openapi.director import RequestDirector
 if TYPE_CHECKING:
     from fastmcp.server import Context
 
+_SAFE_HEADERS = frozenset(
+    {
+        "accept",
+        "accept-encoding",
+        "accept-language",
+        "cache-control",
+        "connection",
+        "content-length",
+        "content-type",
+        "host",
+        "user-agent",
+    }
+)
+
+
+def _redact_headers(headers: httpx.Headers) -> dict[str, str]:
+    return {k: v if k.lower() in _SAFE_HEADERS else "***" for k, v in headers.items()}
+
+
 __all__ = [
     "OpenAPIResource",
     "OpenAPIResourceTemplate",
@@ -183,7 +202,9 @@ class OpenAPITool(Tool):
 
         # Send the request and process the response.
         try:
-            logger.debug(f"run - sending request; headers: {request.headers}")
+            logger.debug(
+                f"run - sending request; headers: {_redact_headers(request.headers)}"
+            )
 
             response = await self._client.send(request)
             response.raise_for_status()
diff --git a/tests/server/providers/openapi/test_openapi_features.py b/tests/server/providers/openapi/test_openapi_features.py
index ef4aeb002..ac78f1b10 100644
--- a/tests/server/providers/openapi/test_openapi_features.py
+++ b/tests/server/providers/openapi/test_openapi_features.py
@@ -9,7 +9,10 @@ from httpx import Response
 from fastmcp import FastMCP
 from fastmcp.client import Client
 from fastmcp.server.providers.openapi import OpenAPIProvider
-from fastmcp.server.providers.openapi.components import _extract_mime_type_from_route
+from fastmcp.server.providers.openapi.components import (
+    _extract_mime_type_from_route,
+    _redact_headers,
+)
 from fastmcp.server.providers.openapi.routing import MCPType, RouteMap
 from fastmcp.utilities.openapi.models import HTTPRoute, ResponseInfo
 
@@ -982,3 +985,45 @@ class TestValidateOutput:
             assert get_user.outputSchema.get("additionalProperties") is True
             # Should NOT have specific properties from the original schema
             assert "properties" not in get_user.outputSchema
+
+
+class TestRedactHeaders:
+    """Test that non-safe headers are redacted in debug logging."""
+
+    def test_known_sensitive_headers_are_redacted(self):
+        headers = httpx.Headers(
+            {
+                "Authorization": "Bearer secret-token",
+                "X-API-Key": "my-api-key",
+                "Cookie": "session=abc123",
+                "Proxy-Authorization": "Basic creds",
+                "Content-Type": "application/json",
+                "Accept": "text/html",
+            }
+        )
+        redacted = _redact_headers(headers)
+        assert redacted["authorization"] == "***"
+        assert redacted["x-api-key"] == "***"
+        assert redacted["cookie"] == "***"
+        assert redacted["proxy-authorization"] == "***"
+        assert redacted["content-type"] == "application/json"
+        assert redacted["accept"] == "text/html"
+
+    def test_arbitrary_auth_headers_are_redacted(self):
+        """Arbitrary header names (e.g. OpenAPI apiKey-in-header) are redacted."""
+        headers = httpx.Headers(
+            {
+                "X-Custom-Token": "secret",
+                "X-My-Service-Key": "also-secret",
+                "Content-Type": "application/json",
+            }
+        )
+        redacted = _redact_headers(headers)
+        assert redacted["x-custom-token"] == "***"
+        assert redacted["x-my-service-key"] == "***"
+        assert redacted["content-type"] == "application/json"
+
+    def test_safe_only_headers(self):
+        headers = httpx.Headers({"Content-Type": "application/json"})
+        redacted = _redact_headers(headers)
+        assert redacted == {"content-type": "application/json"}