security(webhooks): fail closed when no HMAC secret (closes #99)#120
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verify_signature() previously returned True for a webhook with no
hmac_secret ("open mode"). create() auto-mints a secret, but a
hand-written / migrated config (or one whose secret was cleared on disk)
was silently unauthenticated — anonymous POSTs could spawn an AI
assistant with tool access.
- verify_signature now FAILS CLOSED (returns False, logs why) when no
secret is configured.
- KC_ALLOW_UNSIGNED_WEBHOOKS=1 is an explicit opt-in for local/testing.
- _public_view exposes an `unsigned` flag so the dashboard can warn that
a webhook is secret-less and will reject POSTs.
The update path already preserves the prior secret, so normal edits
can't clear it; this closes the hand-edited-config gap.
Tests (tests/server_test.py): fail-closed without secret, open-mode
opt-in, env parsing, and the public-view unsigned flag (webhook suite
18 -> 22). Full suite 470, OK.
Closes #99
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
Makes webhook signature verification fail closed when no HMAC secret is configured. Closes #99 — PR 2 of the reliability-hardening series. (Security)
Why
verify_signature()returnedTruefor a webhook with nohmac_secret("open mode").create()auto-mints a secret, but a hand-written / migrated config — or one whose secret was cleared directly on disk — was silently unauthenticated, so anonymous POSTs could spawn an AI assistant with tool access. That's an RCE-adjacent exposure.Changes
verify_signaturenow fails closed (returnsFalse, logs the reason) when no secret is set.KC_ALLOW_UNSIGNED_WEBHOOKS=1— explicit opt-in to restore open mode for local/testing (off by default)._public_viewexposes anunsignedflag so the dashboard can warn that a webhook is secret-less and will reject POSTs.The update path already preserves the prior secret, so a normal edit can't clear it — this specifically closes the hand-edited-config / migration gap.
Tests
tests/server_test.py: fail-closed without secret, open-mode opt-in,KC_ALLOW_UNSIGNED_WEBHOOKSparsing, and the public-viewunsignedflag (webhook suite 18 → 22). Full Python suite 470, OK.Closes #99
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