CVE-2017-17704 in iStar Ultra
Summary
by MITRE
A door-unlocking issue was discovered on Software House iStar Ultra devices through 6.5.2.20569 when used in conjunction with the IP-ACM Ethernet Door Module. The communications between the IP-ACM and the iStar Ultra is encrypted using a fixed AES key and IV. Each message is encrypted in CBC mode and restarts with the fixed IV, leading to replay attacks of entire messages. There is no authentication of messages beyond the use of the fixed AES key, so message forgery is also possible.
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Analysis
by VulDB Data Team • 12/18/2019
The vulnerability identified as CVE-2017-17704 represents a critical security flaw in Software House iStar Ultra access control systems, specifically affecting versions through 6.5.2.20569. This issue manifests through the integration of the IP-ACM Ethernet Door Module with the iStar Ultra platform, creating a dangerous scenario where physical security can be compromised through digital means. The affected systems are designed for enterprise access control and security management, making this vulnerability particularly concerning for organizations relying on these platforms for physical security infrastructure. The flaw exists in the communication protocol between the door module and the central control system, fundamentally undermining the security model that these systems are meant to provide.
The technical implementation of this vulnerability stems from a fundamental cryptographic weakness in the communication protocol between the IP-ACM module and the iStar Ultra system. The system employs AES encryption with a fixed key and initialization vector IV, which violates core security principles for cryptographic implementations. When messages are encrypted in CBC mode using a static IV, the encryption becomes vulnerable to replay attacks because identical plaintext messages will produce identical ciphertext blocks. This deterministic behavior allows attackers to capture legitimate messages and replay them at will, effectively bypassing the authentication mechanisms. The fixed IV creates a predictable pattern that undermines the security properties of CBC mode, as the same plaintext will always produce the same ciphertext when encrypted with the same key and IV combination. This weakness directly maps to CWE-327, which addresses the use of insecure cryptographic algorithms and improper implementation of encryption protocols.
The operational impact of this vulnerability extends far beyond simple technical concerns, as it fundamentally compromises the physical security of facilities protected by these systems. An attacker with network access can potentially unlock doors without authorization by replaying captured door unlock messages or by forging new messages using the fixed key. This creates a scenario where unauthorized individuals can gain physical access to secured areas, potentially leading to theft, vandalism, or more serious security breaches. The lack of proper message authentication beyond the fixed key means that attackers can not only replay messages but also create entirely new valid messages that appear to originate from legitimate sources within the system. This vulnerability affects the integrity and authenticity properties of the security system, making it possible for attackers to manipulate access control decisions without detection.
Organizations affected by this vulnerability should immediately implement mitigation strategies to address the cryptographic weaknesses in their access control systems. The most effective immediate solution involves replacing the fixed AES key with a dynamically generated key for each communication session, while also implementing proper message authentication codes or digital signatures to verify message integrity and origin. Network segmentation should be implemented to limit access to the affected systems, and monitoring should be deployed to detect anomalous access patterns or repeated message sequences. Security updates should be applied as soon as patches become available from the vendor, though the nature of the vulnerability suggests that a complete redesign of the cryptographic protocol may be necessary. The implementation of additional authentication layers beyond the simple key-based encryption, such as challenge-response mechanisms or time-based tokens, would significantly improve the security posture of these systems.
This vulnerability demonstrates the critical importance of proper cryptographic implementation in security systems, particularly those controlling physical access. The use of fixed cryptographic parameters in security-sensitive applications represents a fundamental flaw that can be exploited to completely bypass the intended security controls. The attack surface is relatively small since it requires network access to the affected systems, but the potential impact is severe due to the direct control over physical access points. The vulnerability also highlights the need for proper security testing and code review processes, particularly for systems handling physical security, where cryptographic flaws can have real-world consequences. From an ATT&CK perspective, this vulnerability maps to privilege escalation and defense evasion techniques, as attackers can use the compromised system to gain unauthorized access to physical locations while remaining undetected by traditional security monitoring systems. The remediation process should include comprehensive security testing of all cryptographic implementations within the access control system to prevent similar vulnerabilities from existing in other components.