CVE-2018-20958 in Tapplock
Summary
by MITRE
The Bluetooth Low Energy (BLE) subsystem on Tapplock devices before 2018-06-12 relies on Key1 and SerialNo for unlock operations; however, these are derived from the MAC address, which is broadcasted by the device.
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Analysis
by VulDB Data Team • 07/22/2020
The vulnerability identified as CVE-2018-20958 represents a critical security flaw in the Bluetooth Low Energy implementation of Tapplock smart locks. This weakness stems from the device's reliance on cryptographic keys derived from the MAC address, creating a fundamental flaw in the authentication mechanism that undermines the security model of the entire locking system. The vulnerability affects all Tapplock devices released prior to June 12, 2018, making them susceptible to unauthorized access through relatively simple exploitation techniques.
The technical implementation of this vulnerability lies in the predictable nature of the key derivation process used by the BLE subsystem. When a Tapplock device broadcasts its MAC address, this information becomes publicly accessible to anyone within range of the device's wireless signal. The system then uses this broadcasted MAC address as the basis for generating Key1 and SerialNo, which are essential components for unlock operations. This design flaw creates a direct correlation between the device's broadcast identifier and its cryptographic security parameters, effectively eliminating the security benefits that should normally be provided by proper key management and authentication protocols.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass broader security implications for physical access control systems. An attacker within Bluetooth range of a vulnerable Tapplock device can potentially extract the MAC address and use it to derive the corresponding unlock keys, thereby gaining access to secured locations without proper authorization. This vulnerability directly violates the principles of secure key management and authentication as outlined in cybersecurity frameworks such as those referenced in CWE-310, which addresses cryptographic weaknesses and the improper use of cryptographic primitives. The attack surface is particularly concerning given that BLE devices typically operate in environments where physical proximity is required for exploitation, making this a viable threat vector for both casual attackers and malicious actors seeking unauthorized physical access.
The security implications of this vulnerability align with ATT&CK framework concepts related to credential access and privilege escalation, as the exploitation process essentially allows attackers to obtain valid authentication credentials through the analysis of publicly broadcast information. This type of vulnerability demonstrates the critical importance of proper key derivation functions and the avoidance of predictable cryptographic inputs in embedded security systems. Organizations relying on Tapplock devices for physical security must consider immediate remediation measures including firmware updates, replacement of affected devices, and potential re-keying of their access control systems to prevent exploitation. The vulnerability also highlights the need for comprehensive security testing of IoT devices before deployment, particularly in environments where physical security is paramount and the consequences of unauthorized access could be significant.