microsoft/semantic-kernel · error · KernelException

The URI scheme '{addressUri.Scheme}' is not allowed for the

Error message

The URI scheme '{addressUri.Scheme}' is not allowed for the '{operation.Name}' gRPC operation. Allowed schemes: {string.Join(", ", this._allowedSchemes)}.

What it means

Thrown when the parsed URI's scheme is not in the configured `_allowedSchemes` allow-list (case-insensitive). This is a security control: it prevents the gRPC runner from connecting via unexpected schemes (e.g. file://, ftp://) that could be smuggled via a malicious address.

Source

Thrown at dotnet/src/Functions/Functions.Grpc/GrpcOperationRunner.cs:185

        else
        {
            address = operation.Address;
        }

        if (string.IsNullOrEmpty(address))
        {
            throw new KernelException($"No address provided for the '{operation.Name}' gRPC operation.");
        }

        if (!Uri.TryCreate(address, UriKind.Absolute, out var addressUri))
        {
            throw new KernelException($"The address '{address}' for the '{operation.Name}' gRPC operation is not a valid absolute URI.");
        }

        // Validate scheme
        if (!this._allowedSchemes.Contains(addressUri.Scheme, StringComparer.OrdinalIgnoreCase))
        {
            throw new KernelException($"The URI scheme '{addressUri.Scheme}' is not allowed for the '{operation.Name}' gRPC operation. Allowed schemes: {string.Join(", ", this._allowedSchemes)}.");
        }

        // Validate against allowed addresses
        if (this._allowedAddresses is { Count: > 0 })
        {
            bool isAllowed = false;
            foreach (var allowedAddress in this._allowedAddresses)
            {
                string allowedUri = allowedAddress.AbsoluteUri;

                if (addressUri.AbsoluteUri.StartsWith(allowedUri, StringComparison.OrdinalIgnoreCase))
                {
                    // If the allowed URI already ends at a boundary (e.g., trailing '/'),
                    // or the full URIs match exactly, no further check is needed.
                    // Otherwise, ensure the next character is a path boundary to prevent
                    // prefix bypasses (e.g., allowed "https://host/grpc" should not match "https://host/grpcevil").
                    int prefixLength = allowedUri.Length;
                    if (prefixLength >= addressUri.AbsoluteUri.Length ||

View on GitHub (pinned to c028a0c7dc)

Solutions

  1. Match the address scheme to the allowed set (prefer https).
  2. If http is intentional and trusted, add it to AllowedSchemes in GrpcOperationRunnerOptions.
  3. Double-check the address override URI scheme.

Example fix

// before
// address = http://service, allowedSchemes = [https]
// after
address = "https://service";
// or, only if http is explicitly trusted:
options.AllowedSchemes = new[] { "http", "https" };
Defensive patterns

Strategy: validation

Validate before calling

var allowed = new[] { "https" };
if (Uri.TryCreate(address, UriKind.Absolute, out var u) && !allowed.Contains(u.Scheme))
    throw new InvalidOperationException($"Scheme {u.Scheme} not allowed.");

Prevention

When it happens

Trigger: Address uses a scheme not in the allowed set — commonly the allow-list contains only `https` (or `http`/`https`) and the address is `http://` in a production-locked config, or vice-versa.

Common situations: Local dev uses plain http but the runner was configured to allow only https; a misconfigured address override carrying the wrong scheme.

Related errors

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/6c9cc1db2fb1a577. Report an issue: GitHub.