microsoft/semantic-kernel · error · FunctionExecutionException

The request URI scheme '{parsed_url.scheme}' is not allowed.

Error message

The request URI scheme '{parsed_url.scheme}' is not allowed. Only '{DEFAULT_ALLOWED_SCHEME}' is permitted by default. To allow this URL, add it to server_url_validation_allowed_base_urls.

What it means

Thrown when allowed_base_urls is empty (no allow-list) and the request URL scheme is not https (DEFAULT_ALLOWED_SCHEME). Without an explicit allow-list, Semantic Kernel only permits HTTPS by default to reduce SSRF and plaintext-exposure risk.

Source

Thrown at python/semantic_kernel/connectors/openapi_plugin/server_url_validator.py:55

    """Validate a fully resolved OpenAPI operation URL against the supplied policy."""
    options = options or ServerUrlValidationOptions()
    try:
        parsed_url = _parse_absolute_url(url)
    except ValueError as exc:
        raise FunctionExecutionException(
            f"The request URI '{url}' is not allowed because it is not a valid absolute URI."
        ) from exc

    if _matches_allowed_base_url(parsed_url, options.allowed_base_urls):
        return

    if options.allowed_base_urls:
        raise FunctionExecutionException(
            f"The request URI '{url}' is not allowed. It does not match any of the allowed base URLs."
        )

    if parsed_url.scheme.lower() != DEFAULT_ALLOWED_SCHEME:
        raise FunctionExecutionException(
            f"The request URI scheme '{parsed_url.scheme}' is not allowed. "
            f"Only '{DEFAULT_ALLOWED_SCHEME}' is permitted by default. "
            "To allow this URL, add it to server_url_validation_allowed_base_urls."
        )

    if options.allow_private_network_access:
        return

    await _ensure_public_host(parsed_url, dns_resolver)


def try_categorize_non_public_address(
    address: str | ipaddress.IPv4Address | ipaddress.IPv6Address,
) -> tuple[bool, str]:
    """Return whether an IP address is non-public and the category when blocked."""
    ip_address = ipaddress.ip_address(address)

    if isinstance(ip_address, ipaddress.IPv6Address) and ip_address.ipv4_mapped:

View on GitHub (pinned to c028a0c7dc)

Solutions

Switch the OpenAPI server URL to https://
If plain HTTP is required for a trusted host, add its full base URL (including the http scheme) to allowed_base_urls
Set allow_private_network_access=True only when you intentionally target a private/loopback host over http

Example fix

# before - spec server: http://localhost:8080
await validate_server_url('http://localhost:8080/api/run')  # raises 1501

# after - allow the explicit http base
options = ServerUrlValidationOptions(allowed_base_urls=['http://localhost:8080/api'])
await validate_server_url('http://localhost:8080/api/run', options)

Defensive patterns

Strategy: validation

Validate before calling

from urllib.parse import urlparse

def is_https_or_allowed(url: str, allowed_base_urls: list[str]) -> bool:
    scheme = urlparse(url).scheme.lower()
    return scheme == 'https' or any(urlparse(url).scheme.lower() == urlparse(b).scheme.lower() for b in allowed_base_urls)

if not is_https_or_allowed(url, options.allowed_base_urls):
    # force https or add an explicit http base to the allow-list
    url = url.replace('http://', 'https://', 1) if not options.allowed_base_urls else url

Try / catch

try:
    await validate_server_url(url, options)
except FunctionExecutionException as e:
    if 'permitted by default' in str(e):
        # either upgrade to https or add the http base url to allowed_base_urls
        ...

Prevention

Author OpenAPI specs against https server URLs
In local dev, add the explicit http base URL to allowed_base_urls rather than weakening defaults
Avoid ftp/file schemes for plugin operations

When it happens

Trigger: An OpenAPI plugin server URL uses a non-https scheme (http://, ftp://) and no allowed_base_urls were configured. Common: http://localhost:8080 or http://internal-service in the spec.

Common situations: Local development over plain HTTP; internal services without TLS; OpenAPI spec authored against http://; CI environment without TLS termination.

Related errors

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/ac2fde0509a44030. Report an issue: GitHub.