fix(validators): allow brackets in query parameters while blocking IPv6 addresses

.secrets.baseline

@@ -3,7 +3,7 @@
     "files": "(?x)( package-lock\\.json$ |Cargo\\.lock$ |uv\\.lock$ |go\\.sum$ |mcpgateway/sri_hashes\\.json$ )|^.secrets.baseline$",
     "lines": null
   },
-  "generated_at": "2026-05-05T12:37:46Z",
+  "generated_at": "2026-05-04T09:02:11Z",
   "plugins_used": [
     {
       "name": "AWSKeyDetector"
@@ -9706,7 +9706,7 @@
         "hashed_secret": "9d4e1e23bd5b727046a9e3b4b7db57bd8d6ee684",
         "is_secret": false,
         "is_verified": false,
-        "line_number": 1142,
+        "line_number": 1151,
         "type": "Basic Auth Credentials",
         "verified_result": null
       }

mcpgateway/common/validators.py

@@ -1240,12 +1240,6 @@ def validate_url(cls, value: str, field_name: str = "URL") -> str:
             if pattern.search(decoded_value):
                 raise ValueError(f"{field_name} contains unsupported or potentially dangerous protocol")
 
-        # Block IPv6 URLs (square brackets). Scanning `decoded_value` alone
-        # suffices: unquote() never removes non-`%` chars, so any `[` in
-        # `value` also appears in `decoded_value`; `%5B` adds a `[` only there.
-        if "[" in decoded_value or "]" in decoded_value:
-            raise ValueError(f"{field_name} contains IPv6 address which is not supported")
-
         # Block protocol-relative URLs
         if value.startswith("//"):
             raise ValueError(f"{field_name} contains protocol-relative URL which is not supported")
@@ -1275,6 +1269,11 @@ def validate_url(cls, value: str, field_name: str = "URL") -> str:
             # urlparse does not decode netloc; decode to catch `exam%20ple.com`-style
             # authority injection without breaking encoded-space in path/query.
             decoded_netloc = _unquote_if_needed(result.netloc)
+
+            # Check for brackets in decoded netloc (catches URL-encoded IPv6 like %5B::1%5D)
+            if "[" in decoded_netloc or "]" in decoded_netloc:
+                raise ValueError(f"{field_name} contains IPv6 address which is not supported")
+
             if any(ch.isspace() for ch in decoded_netloc):
                 raise ValueError(f"{field_name} contains spaces which are not allowed in URLs")
 

tests/unit/mcpgateway/validation/test_validators_advanced.py

@@ -1124,6 +1124,15 @@ class TestValidateUrlSecurity:
     def test_ipv6_blocked(self):
         with pytest.raises(ValueError, match="IPv6"):
             SecurityValidator.validate_url("https://[::1]/path")
+    def test_brackets_in_query_params_allowed(self):
+        """Brackets in query parameters should be allowed (common API pattern)."""
+        # URL-encoded brackets in query params (Laravel, Spring, OData, JSON:API style)
+        assert SecurityValidator.validate_url("https://api.example.com/ingredients?filter%5Bname%5D=value", "URL")
+        assert SecurityValidator.validate_url("https://api.example.com/items?sort%5B0%5D=name&sort%5B1%5D=created_at", "URL")
+        assert SecurityValidator.validate_url("https://api.example.com/data?include%5B%5D=relation", "URL")
+        # Literal brackets in query params (if not URL-encoded by client)
+        assert SecurityValidator.validate_url("https://api.example.com/items?filter[status]=active", "URL")
+
 
     def test_crlf_injection(self):
         with pytest.raises(ValueError, match="control characters"):