CVE-2018-7296 in Homematic CCU2
Summary
by MITRE
Directory Traversal / Arbitrary File Read in User.getLanguage method in eQ-3 AG Homematic CCU2 2.29.2 and earlier allows remote attackers to read the first line of an arbitrary file on the CCU2's filesystem. This vulnerability can be exploited by unauthenticated attackers with access to the web interface.
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Analysis
by VulDB Data Team • 01/08/2020
The vulnerability identified as CVE-2018-7296 represents a critical directory traversal flaw within the eQ-3 AG Homematic CCU2 firmware version 2.29.2 and earlier. This security weakness resides in the User.getLanguage method implementation, which fails to properly validate user input parameters before processing file access requests. The flaw enables remote attackers to manipulate the application's file handling mechanisms and retrieve the first line of any file located within the CCU2's filesystem, potentially exposing sensitive configuration data, authentication credentials, or system information. The vulnerability specifically affects the web interface component of the Homematic CCU2 device, which serves as the primary management interface for users to configure and monitor their smart home automation systems.
The technical implementation of this vulnerability stems from inadequate input sanitization within the User.getLanguage method, which processes language parameter values without proper validation or restriction. When an attacker submits a maliciously crafted language parameter containing directory traversal sequences such as "../", the system fails to sanitize this input before using it in file access operations. This allows the application to interpret the crafted path and return the first line of the targeted file, effectively bypassing normal file access controls. The vulnerability is classified as a directory traversal attack pattern that aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal. The flaw demonstrates a classic security weakness in input validation and file access control mechanisms, where user-supplied data directly influences the application's file system operations without adequate sanitization.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with potentially sensitive data that could facilitate further exploitation attempts. The ability to read the first line of arbitrary files means that attackers could potentially extract configuration parameters, system identifiers, or even partial credential information from files such as configuration files, log files, or system databases. This information disclosure vulnerability can significantly weaken the overall security posture of the Homematic CCU2 system, as it provides attackers with insights into the device's internal structure and potentially sensitive operational details. The unauthenticated nature of the attack means that any remote user with access to the web interface can exploit this vulnerability, making it particularly dangerous as it requires no prior authorization or credentials to initiate the attack. The vulnerability affects the core management functionality of the device, potentially compromising the entire smart home automation ecosystem that relies on the CCU2 as its central control unit.
The security implications of CVE-2018-7296 align with several ATT&CK framework techniques, particularly those related to credential access and reconnaissance activities. Attackers could leverage this vulnerability to gather intelligence about the target environment and potentially identify additional attack vectors. The flaw represents a fundamental breakdown in the principle of least privilege, where user input should never directly influence file system operations without proper validation. Organizations using affected Homematic CCU2 devices should implement immediate mitigations including firmware updates to version 2.30.17 or later, which contain the necessary patches to address the directory traversal vulnerability. Network segmentation and access control measures should be implemented to limit exposure of the web interface to trusted networks only. Additionally, regular monitoring of system logs for suspicious activity and implementation of intrusion detection systems can help identify potential exploitation attempts. The vulnerability underscores the critical importance of proper input validation and secure coding practices in embedded systems, particularly those handling sensitive user data and providing network access to critical infrastructure components.