Python: normalize OpenAPI allowlist paths before prefix match

Decode %2e/%2E and apply RFC 3986 remove_dot_segments so
allowed_base_urls cannot be escaped with .. or encoded dots.
Matches httpx path normalization; empty segments preserved.

Fixes #14662

Author: mangeshraut712

python/semantic_kernel/connectors/openapi_plugin/server_url_validator.py

@@ -113,9 +113,51 @@ def _effective_port(url: ParseResult) -> int | None:
     return None
 
 
+def _normalize_path(path: str) -> str:
+    """Normalize a URL path the same way httpx does before routing.
+
+    Applies RFC 3986 §5.2.4 remove_dot_segments after decoding percent-encoded
+    ``.`` / ``..`` segments (``%2e`` / ``%2E``). Other percent-encodings are left
+    intact. Empty segments are preserved. Paths that would climb above the root
+    are clamped at ``/``.
+    """
+    # Decode only %2e / %2E (dot) so encoded dot-segments resolve; leave other
+    # encodings untouched so allowlist matching stays literal for them.
+    decoded = ""
+    i = 0
+    lower = path.lower()
+    while i < len(path):
+        if lower[i : i + 3] == "%2e":
+            decoded += "."
+            i += 3
+        else:
+            decoded += path[i]
+            i += 1
+
+    # remove_dot_segments (RFC 3986 §5.2.4), preserving empty segments like httpx.
+    segments = decoded.split("/")
+    resolved: list[str] = []
+    for segment in segments:
+        if segment == ".":
+            continue
+        if segment == "..":
+            if resolved and resolved[-1] != "":
+                resolved.pop()
+            # else: clamp at root (leading empty from absolute path stays)
+            continue
+        resolved.append(segment)
+    # Absolute paths keep a leading empty segment from the initial "/".
+    if not resolved:
+        return "/"
+    normalized = "/".join(resolved)
+    if decoded.startswith("/") and not normalized.startswith("/"):
+        normalized = "/" + normalized
+    return normalized or "/"
+
+
 def _matches_path_prefix(url_path: str, base_path: str) -> bool:
-    url_path = url_path or "/"
-    base_path = base_path or "/"
+    url_path = _normalize_path(url_path or "/")
+    base_path = _normalize_path(base_path or "/")
 
     if url_path.lower() == base_path.lower():
         return True

python/tests/unit/connectors/openapi_plugin/test_server_url_validator.py

@@ -241,3 +241,42 @@ async def test_validate_server_url_returns_no_addresses_for_allowed_base_url():
 async def test_validate_server_url_returns_no_addresses_when_private_access_is_allowed():
     options = ServerUrlValidationOptions(allow_private_network_access=True)
     assert await validate_server_url("https://internal.example/api", options) == []
+
+
+@pytest.mark.parametrize(
+    "url",
+    [
+        "https://api.example.com/api/../admin",
+        "https://api.example.com/api/%2e%2e/admin",
+        "https://api.example.com/api/%2E%2E/admin",
+        "https://api.example.com/api/foo/../../admin",
+    ],
+)
+async def test_validate_server_url_rejects_path_prefix_escape(url):
+    """Dot-segment escapes must not satisfy an /api allowlist prefix."""
+    options = ServerUrlValidationOptions(allowed_base_urls=["https://api.example.com/api"])
+
+    with pytest.raises(FunctionExecutionException, match="allowed base URLs"):
+        await validate_server_url(url, options)
+
+
+@pytest.mark.parametrize(
+    "url",
+    [
+        "https://api.example.com/api/./users",
+        "https://api.example.com/api/users",
+        "https://api.example.com/api/",
+        "https://api.example.com/api",
+    ],
+)
+async def test_validate_server_url_allows_normalized_paths_under_prefix(url):
+    options = ServerUrlValidationOptions(allowed_base_urls=["https://api.example.com/api"])
+
+    assert await validate_server_url(url, options) == []
+
+
+async def test_validate_server_url_still_rejects_path_that_only_shares_prefix_chars():
+    options = ServerUrlValidationOptions(allowed_base_urls=["https://api.example.com/api"])
+
+    with pytest.raises(FunctionExecutionException, match="allowed base URLs"):
+        await validate_server_url("https://api.example.com/apiusers", options)