iflytek/astron-agent · error · RemoteResourcePolicyError

Remote resource URL authority is invalid

Error message

Remote resource URL authority is invalid

What it means

RemoteResourcePolicyError raised by _validate_parsed_resource_url when the URL's netloc (authority) contains a backslash character. The SSRF-safe download module in safe_download.py rejects backslashes in the authority because different HTTP parsers handle '\\' inconsistently, which can let an attacker smuggle a hostname past validation (e.g. 'https://example.com\\@evil.com/'). The check runs after scheme, hostname, and user-info checks during URL parsing.

Solutions

1. Remove or percent-encode backslashes from the URL before passing it to fetch_public_resource; build URLs with yarl.URL instead of string concatenation
2. Validate/sanitize the caller-supplied URL on the input side (reject or encode '\\' before it reaches the download path)
3. If the backslash is part of a path (not the authority), ensure it is properly placed after the host and percent-encoded as %5C

Example fix

// before
url = f"https://{windows_path}"  # e.g. https://cdn\\host/file
await fetch_public_resource(url)
// after
from yarl import URL
safe = str(URL(f"https://cdn.example.com/{windows_path.replace('\\', '/')}").with_scheme('https'))
await fetch_public_resource(safe)

def is_safe_url_authority(url: str) -> bool:
    from urllib.parse import urlsplit
    try:
        netloc = urlsplit(url).netloc
    except ValueError:
        return False
    return bool(netloc) and "\\" not in netloc and url.isprintable()

def has_clean_authority(url: str) -> bool:
    from urllib.parse import urlsplit
    return "\\" not in urlsplit(url).netloc

from plugin.aitools.common.clients.safe_download import RemoteResourcePolicyError
try:
    data = await fetch_public_resource(url)
except RemoteResourcePolicyError as e:
    log.warning("Rejected URL authority: %s", e)

When it happens

Trigger: Passing a URL string to fetch_public_resource() (or any caller of _parse_resource_url) whose authority segment contains a literal backslash, e.g. 'https://bad\\host.example.com/file' or 'https://trusted.com\\@attacker.com/x'.

Common situations: User-supplied file URLs built by string concatenation where a Windows-style path fragment (C:\\...) leaks into the host portion; LLM/tool output containing escaped characters; template interpolation that injects backslashes into the URL before download.

Understand the failure class

Background: "Invalid URL" errors: why new URL(), URI.parse, and reqwest::Url reject your string — missing scheme, whitespace, and bad path format — this error's family across 39 libraries.

Related errors

• HTTPClientError
• Remote resource URL must not include a fragment
• Skill resource URL is not allowed
• MODEL_URL_CHECK_FAILED
• MODEL_URL_CHECK_FAILED

AI-assisted analysis of iflytek/astron-agent@5e758547a8 (2026-09-12). Data as JSON: /api/errors/d1b43bdf8f2132e3. Report an issue: GitHub.

Appendix: source

Thrown at core/plugin/aitools/common/clients/safe_download.py:219

        raise RemoteResourcePolicyError("Remote resource URL is malformed")


def _validate_parsed_resource_url(
    parsed: SplitResult,
    port: Optional[int],
) -> None:
    if parsed.scheme.lower() not in _ALLOWED_SCHEMES:
        raise RemoteResourcePolicyError(
            "Only HTTP and HTTPS remote resources are allowed"
        )
    if not parsed.hostname:
        raise RemoteResourcePolicyError("Remote resource URL must include a hostname")
    if parsed.username is not None or parsed.password is not None:
        raise RemoteResourcePolicyError(
            "Remote resource URL must not include user information"
        )
    if "\\" in parsed.netloc:
        raise RemoteResourcePolicyError("Remote resource URL authority is invalid")
    if parsed.fragment:
        raise RemoteResourcePolicyError(
            "Remote resource URL must not include a fragment"
        )
    if port is not None and not 1 <= port <= 65535:
        raise RemoteResourcePolicyError("Remote resource URL port is invalid")


def _normalize_hostname(hostname: str) -> str:
    value = hostname.strip().lower().rstrip(".")
    if _parse_ip(value) is not None:
        return value
    try:
        normalized = URL.build(scheme="http", host=value).raw_host
    except (TypeError, ValueError, UnicodeError) as exc:
        raise RemoteResourcePolicyError("Remote resource hostname is invalid") from exc
    if not normalized:
        raise RemoteResourcePolicyError("Remote resource hostname is invalid")

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