fix(security): denylist ~/.hermes/mcp-tokens/ for media delivery - #56163
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mcp-tokens/ holds live MCP OAuth access tokens (<server>.json) and dynamically-registered OAuth client credentials (<server>.client.json), layout per tools/mcp_oauth.py. This is the same credential class as auth.json/credentials/, which _media_delivery_denied_paths() already blocks. The write side already denies this dir (file_tools _check_sensitive_path), but the media-delivery (read/exfil) side did not, leaving an unpaired half-door. Without it, a prompt-injection MEDIA: tag emitting ~/.hermes/mcp-tokens/<server>.json would, in default (non-strict) mode, pass the denylist and exfiltrate a live OAuth bearer token to the same untrusted channel. Sibling follow-up to commit 4ec0ade (config.yaml media-delivery denylist). mcp-tokens is a directory and _path_under_denied_prefix already does containment matching, so the whole subtree (.json/.client.json/ .meta.json) is denied, mirroring credentials/.
alt-glitch
added
type/security
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Salvage of #37222 by @briandevans — related, not a duplicate. Part of the media-delivery credential denylist family: #50912, #51453, #32090. |
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13 tasks
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Summary
Media delivery can no longer auto-attach a live MCP OAuth bearer token.
mcp-tokens/is now on the media-delivery denylist, pairing the exfil side with the read/write guard that already blocked it.Salvage of #37222 by @briandevans, cherry-picked onto current
mainwith authorship preserved.Root cause:
_media_delivery_denied_paths()ingateway/platforms/base.pydenied.env,auth.json,credentials/,config.yaml, andpairing/— but notmcp-tokens/. The read/write guard (agent/file_safety.py) already denied that directory, so the delivery/exfil side trailed the write side. A prompt-injectionMEDIA:~/.hermes/mcp-tokens/github.jsontag would, in default (non-strict) mode, deliver a live bearer token as a native gateway attachment.Changes
gateway/platforms/base.py: add"mcp-tokens"to_ROOT_CREDENTIAL_DIRS. Directory-prefix containment (_path_is_within) seals the whole subtree (<server>.json/.client.json/.meta.json), mirroringpairing/. Comment updated (the old text pointed at this PR as the pending sibling).tests/gateway/test_platform_base.py: parametrized test assertingvalidate_media_delivery_pathreturnsNonefor the three token file types.Validation
MEDIA:mcp-tokens/github.jsonNone(denied)pairing/,auth.jsoncache/images/*.pngscripts/run_tests.sh tests/gateway/test_platform_base.py→ 177/177 pass (3 new cases).HERMES_HOME: all three token files DENIED, control siblings still denied, fresh cache image still delivers.Infographic
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