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fix(security): denylist ~/.hermes/mcp-tokens/ for media delivery #37222

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fix(security): denylist ~/.hermes/mcp-tokens/ for media delivery #37222

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14 changes: 10 additions & 4 deletions gateway/platforms/base.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1134,12 +1134,18 @@ def _media_delivery_denied_paths() -> List[Path]:
# Bitwarden Secrets Manager plaintext disk cache.
os.path.join("cache", "bws_cache.json"),
)
# Directory trees whose every child is credential material. (MCP OAuth
# tokens under mcp-tokens/ are handled by the sibling targeted PR #37222;
# session/kanban SQLite stores by #41071 — kept out of this diff to avoid
# overlap.)
# Directory trees whose every child is credential material.
#
# mcp-tokens/ holds live MCP OAuth access tokens (<server>.json) and
# dynamically-registered client credentials (<server>.client.json); see
# tools/mcp_oauth.py. Same credential class as auth.json/credentials/.
# The write side already denies it (file_tools _check_sensitive_path);
# this pairs the media-delivery (exfil) side so a prompt-injection MEDIA
# tag can't deliver a live bearer token as a native attachment.
# (session/kanban SQLite stores are handled by #41071 — kept out here.)
_ROOT_CREDENTIAL_DIRS = (
"pairing",
"mcp-tokens",
)
for hermes_root in (_HERMES_HOME, _HERMES_ROOT):
for rel in _ROOT_CREDENTIAL_FILES:
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32 changes: 32 additions & 0 deletions tests/gateway/test_platform_base.py
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Expand Up @@ -928,6 +928,38 @@ def test_denylist_blocks_hermes_credentials(self, tmp_path, monkeypatch):

assert BasePlatformAdapter.validate_media_delivery_path(str(env_file)) is None

@pytest.mark.parametrize(
"rel",
[
"mcp-tokens/github.json",
"mcp-tokens/github.client.json",
"mcp-tokens/github.meta.json",
],
)
def test_denylist_blocks_mcp_oauth_tokens(self, tmp_path, monkeypatch, rel):
"""Live MCP OAuth tokens/client creds under ~/.hermes/mcp-tokens/ must
never deliver as native media — same exfil class as auth.json/.env.
Sibling to the pairing/ directory denylist entry.
"""
self._patch_roots(monkeypatch)

fake_home = tmp_path / "home"
hermes_dir = fake_home / ".hermes"
(hermes_dir / "mcp-tokens").mkdir(parents=True)
secret = hermes_dir / rel
secret.write_text('{"access_token": "live-bearer-abc123"}')
monkeypatch.setenv("HOME", str(fake_home))
monkeypatch.setattr(
"gateway.platforms.base._HERMES_HOME",
hermes_dir,
)
monkeypatch.setattr(
"gateway.platforms.base._HERMES_ROOT",
hermes_dir,
)

assert BasePlatformAdapter.validate_media_delivery_path(str(secret)) is None

def test_denylist_blocks_hermes_config_in_active_profile(self, tmp_path, monkeypatch):
"""The active profile config stays blocked in default mode."""
self._patch_roots(monkeypatch)
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