mirror of
https://github.com/NousResearch/hermes-agent.git
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100 lines
3.7 KiB
Python
100 lines
3.7 KiB
Python
"""Security policy for credential-bearing stdlib urllib requests."""
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from __future__ import annotations
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import copy
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import urllib.parse
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import urllib.request
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from collections.abc import Callable, Iterable
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from typing import Any
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# Headers safe to forward to a different origin. Everything else is dropped:
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# custom provider headers routinely carry credentials under arbitrary names.
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_CROSS_ORIGIN_SAFE_HEADERS = frozenset({"accept", "user-agent"})
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_DEFAULT_PORTS = {"http": 80, "https": 443}
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def url_origin(url: str) -> tuple[str, str, int | None]:
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"""Return a normalized (scheme, hostname, effective port) origin."""
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parsed = urllib.parse.urlparse(url)
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scheme = (parsed.scheme or "").lower()
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# Accessing ``parsed.port`` validates malformed/non-numeric ports. Let the
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# ValueError fail the request closed instead of collapsing it to a default.
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port = parsed.port
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return (
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scheme,
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(parsed.hostname or "").lower().rstrip("."),
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port if port is not None else _DEFAULT_PORTS.get(scheme),
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)
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class SafeCredentialRedirectHandler(urllib.request.HTTPRedirectHandler):
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"""Preserve request headers only while redirects stay on one origin."""
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def __init__(
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self,
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original_url: str,
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*,
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cross_origin_safe_headers: Iterable[str] = _CROSS_ORIGIN_SAFE_HEADERS,
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) -> None:
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self._original_origin = url_origin(original_url)
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self._cross_origin_safe_headers = frozenset(
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str(name).lower() for name in cross_origin_safe_headers
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)
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def redirect_request(self, req, fp, code, msg, headers, newurl):
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# Let urllib enforce status/method semantics first (notably 307/308).
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redirected = super().redirect_request(req, fp, code, msg, headers, newurl)
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if redirected is None:
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return None
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resolved_url = urllib.parse.urljoin(req.full_url, newurl)
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if url_origin(resolved_url) != self._original_origin:
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# Use an allowlist rather than guessing credential header names.
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# normalize_extra_headers permits arbitrary secret-bearing names.
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for name, _value in list(redirected.header_items()):
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if name.lower() not in self._cross_origin_safe_headers:
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redirected.remove_header(name)
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return redirected
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def _secure_opener_from_installed_policy(original_url: str):
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"""Clone the installed opener's handlers, replacing redirect policy only."""
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installed = getattr(urllib.request, "_opener", None)
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if installed is None:
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installed = urllib.request.build_opener()
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handlers = [
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copy.copy(handler)
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for handler in getattr(installed, "handlers", ())
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if not isinstance(handler, urllib.request.HTTPRedirectHandler)
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]
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handlers.append(SafeCredentialRedirectHandler(original_url))
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return urllib.request.build_opener(*handlers)
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def open_credentialed_url(
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request: urllib.request.Request,
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*,
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timeout: float,
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opener_factory: Callable[..., Any] | None = None,
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):
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"""Open a request without forwarding credentials across origins.
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The default preserves an application-installed opener's proxy, TLS,
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cookies, custom protocol handlers, and instrumentation while replacing its
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redirect handler. ``opener_factory`` is an explicit test seam; security is
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never disabled based on global ``urlopen`` identity.
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"""
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if opener_factory is None:
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opener = _secure_opener_from_installed_policy(request.full_url)
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else:
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opener = opener_factory(SafeCredentialRedirectHandler(request.full_url))
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return opener.open(request, timeout=timeout)
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__all__ = [
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"SafeCredentialRedirectHandler",
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"open_credentialed_url",
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"url_origin",
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]
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