CVE-2017-16778 in Outdoor Panel
Summary
by MITRE
An access control weakness in the DTMF tone receiver of Fermax Outdoor Panel allows physical attackers to inject a Dual-Tone-Multi-Frequency (DTMF) tone to invoke an access grant that would allow physical access to a restricted floor/level. By design, only a residential unit owner may allow such an access grant. However, due to incorrect access control, an attacker could inject it via the speaker unit to perform an access grant to gain unauthorized access, as demonstrated by a loud DTMF tone representing '1' and a long '#' (697 Hz and 1209 Hz, followed by 941 Hz and 1477 Hz).
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Analysis
by VulDB Data Team • 12/25/2019
The vulnerability described in CVE-2017-16778 represents a critical access control weakness within the DTMF tone receiver of Fermax Outdoor Panel systems, fundamentally compromising the security model of physical access control infrastructure. This flaw exists in the authentication and authorization mechanisms of residential access control systems, where the expected security boundary is that only legitimate unit owners can grant access to restricted areas. The system's design relies on DTMF tones as a legitimate access control method, but fails to implement proper validation and authorization checks for incoming tone sequences.
The technical implementation of this vulnerability stems from inadequate input validation and access control enforcement within the DTMF receiver component. The system processes DTMF tones without proper authentication verification, allowing any physical attacker with access to the speaker unit to inject malicious DTMF sequences that bypass normal access control procedures. The specific attack vector involves generating a loud DTMF tone sequence representing '1' followed by a long '#', which translates to specific frequency combinations of 697 Hz and 1209 Hz, followed by 941 Hz and 1477 Hz. This sequence corresponds to the standard DTMF encoding for the digit '1' and the pound key, which the system incorrectly interprets as a legitimate access grant command from an authorized user.
The operational impact of this vulnerability extends beyond simple unauthorized access, representing a fundamental breakdown in physical security infrastructure that could enable various malicious activities. An attacker could exploit this weakness to gain access to restricted floors or levels within multi-occupancy residential buildings, potentially leading to property theft, privacy violations, or even physical harm to residents. The vulnerability is particularly concerning because it requires only physical proximity to the speaker unit and does not necessitate sophisticated technical skills or specialized equipment beyond basic audio generation capabilities. This makes the attack surface extremely broad and the exploitation risk high.
This vulnerability maps directly to CWE-284 Access Control Weakness, specifically addressing inadequate access control mechanisms and improper authorization enforcement in the DTMF tone processing component. The flaw also aligns with ATT&CK technique T1210 Exploitation of Remote Services, as it represents an unauthorized access method that exploits a legitimate communication channel within the access control system. The security implications extend to broader physical security frameworks where the integrity of access control systems is paramount, as this vulnerability demonstrates how a single component failure can compromise entire building security infrastructures. Organizations implementing such systems must consider the cascading effects of this type of vulnerability on overall security posture and the potential for similar flaws in related access control components.
Mitigation strategies for this vulnerability should include implementing proper access control validation for all incoming DTMF tones, requiring multi-factor authentication for access grant commands, and ensuring that only authorized sequences from legitimate sources can trigger access control actions. System designers should incorporate robust input validation mechanisms that verify the source and authenticity of DTMF sequences, potentially through cryptographic signatures or time-based authentication tokens. Additionally, physical security measures such as securing speaker units and implementing audio monitoring systems can help detect and prevent unauthorized tone injection attempts. Regular security assessments of access control systems should include testing for similar access control weaknesses and proper validation of all user authentication mechanisms.