modelcontextprotocol/servers · error · Error

Domain is not in the allowed domains list.

Error message

Domain ${domain} is not in the allowed domains list.

What it means

Thrown by `validateDataURI` when the `GZIP_ALLOWED_DOMAINS` env var is set (non-empty) and the http/https URL's hostname is neither an exact match nor a subdomain of any allowed domain. This is an SSRF-control allowlist; an empty env disables the check entirely.

Solutions

1. Add the exact hostname (and any subdomain-bearing parent) to `GZIP_ALLOWED_DOMAINS`, e.g. `example.com,raw.githubusercontent.com`.
2. Use a URL whose host is already in the allowlist or a subdomain of one.
3. To disable domain filtering entirely, leave `GZIP_ALLOWED_DOMAINS` unset/empty (recognize the security trade-off).

Example fix

# before
GZIP_ALLOWED_DOMAINS=example.com
toolHandler({ data: 'https://raw.githubusercontent.com/x/y/z.md' })
# after
GZIP_ALLOWED_DOMAINS=example.com,raw.githubusercontent.com
toolHandler({ data: 'https://raw.githubusercontent.com/x/y/z.md' })

const ALLOWED = (process.env.GZIP_ALLOWED_DOMAINS ?? '').split(',').map(d=>d.trim().toLowerCase()).filter(Boolean);
function domainAllowed(url: string): boolean {
  if (ALLOWED.length === 0) return true;
  const h = new URL(url).hostname.toLowerCase();
  return ALLOWED.some(a => h === a || h.endsWith('.' + a));
}
if (!domainAllowed(args.data)) { /* surface error */ }

When it happens

Trigger: Operator set `GZIP_ALLOWED_DOMAINS=example.com,github.com` and the tool is called with a URL whose host is e.g. `evil.com` or `notgithub.com` (which is not a subdomain match). The check uses exact hostname match or `.endsWith('.' + allowed)`.

Common situations: Misconfigured allowlist (forgot a domain), URL using a bare host vs `www.` variant that isn't covered, or a CDN/redirect domain not in the list. Note: only `endsWith("." + allowed)` — so `evil-example.com` is correctly rejected, but operators must list every domain they intend to permit.

Related errors

• Content-Length for exceeds max of
• Response from exceeds bytes
• Unsupported URL protocol for
• Access denied - parent directory outside allowed directories
• Access denied - path outside allowed directories

AI-assisted analysis of modelcontextprotocol/servers@76d64c822f (2026-08-12). Data as JSON: /api/errors/1cd16567103d87a4. Report an issue: GitHub.

Appendix: source

Thrown at src/everything/tools/gzip-file-as-resource.ts:157

    if (
      url.protocol !== "http:" &&
      url.protocol !== "https:" &&
      url.protocol !== "data:"
    ) {
      throw new Error(
        `Unsupported URL protocol for ${dataUri}. Only http, https, and data URLs are supported.`
      );
    }
    if (
      GZIP_ALLOWED_DOMAINS.length > 0 &&
      (url.protocol === "http:" || url.protocol === "https:")
    ) {
      const domain = url.hostname;
      const domainAllowed = GZIP_ALLOWED_DOMAINS.some((allowedDomain) => {
        return domain === allowedDomain || domain.endsWith(`.${allowedDomain}`);
      });
      if (!domainAllowed) {
        throw new Error(`Domain ${domain} is not in the allowed domains list.`);
      }
    }
  } catch (error) {
    throw new Error(
      `Error processing file ${dataUri}: ${
        error instanceof Error ? error.message : String(error)
      }`
    );
  }
  return url;
}

/**
 * Fetches data safely from a given URL while ensuring constraints on maximum byte size and timeout duration.
 *
 * @param {URL} url The URL to fetch data from.
 * @param {Object} options An object containing options for the fetch operation.
 * @param {number} options.maxBytes The maximum allowed size (in bytes) of the response. If the response exceeds this size, the operation will be aborted.

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