An unauthenticated remote actor can inject an arbitrary ML-KEM‑768 public key into any tenant’s staff‑crypto recipient directory in OpenReception’s appointment booking software. This bypasses the designed guarantee that only registered staff members receive appointment data, enabling the attacker to receive the same encrypted tunnel key used for all future appointments and to decrypt that data with the matching secret key. The flaw represents an authorization bypass, allowing persistent, unauthorized access to confidential information. The vulnerability is scored moderate (CVSS 5.3) and is not yet listed in CISA’s KEV catalog. Its exploitation does not require privileged credentials; the private endpoint accepting the key upload is publicly accessible.

All instances of open-reception:appointment-booking-software with version 2.1.0 or earlier are affected. The flaw affects all tenants, as any tenant’s staff‑crypto directory can be written to by an unauthenticated user. No later versions or other products are mentioned in the advisory.

The lack of authentication for the key upload endpoint means that a remote attacker can inject a malicious key simply by sending a correctly formatted request. Once injected, the attacker becomes a permanent, unauthorized recipient of every appointment encrypted for that tenant, compromising confidentiality on a long‑term basis. The current EPSS score is not available, so the prevalence of exploitation is unknown. The CVSS score indicates a moderate threat, but the persistence nature and lack of patch availability increase risk for organizations that rely on end‑to‑end encryption.