CVE-2018-7539 in XC5000
Summary
by MITRE
On Appear TV XC5000 and XC5100 devices with firmware 3.26.217, it is possible to read OS files with a specially crafted HTTP request (such as GET /../../../../../../../../../../../../etc/passwd) to the web server (fuzzd/0.1.1) running the Maintenance Center on port TCP/8088. This can lead to full compromise of the device.
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Analysis
by VulDB Data Team • 01/25/2020
The vulnerability identified as CVE-2018-7539 represents a critical directory traversal flaw affecting Appear TV XC5000 and XC5100 set-top box devices running firmware version 3.26.217. This security weakness resides within the web server component known as fuzzd/0.1.1 which operates on TCP port 8088 and serves the Maintenance Center interface. The flaw stems from inadequate input validation and path sanitization within the HTTP request processing mechanism, allowing malicious actors to exploit the system through carefully constructed requests that manipulate file path resolution. The vulnerability is classified under CWE-22 as a directory traversal attack, specifically involving improper limitation of a pathname to a restricted directory, which enables unauthorized access to sensitive system files and directories.
The technical exploitation of this vulnerability occurs through HTTP GET requests containing malicious path traversal sequences such as the example provided with the request pattern GET /../../../../../../../../../../../../etc/passwd. This type of attack leverages the web server's failure to properly validate and sanitize user-supplied input before processing file system requests. When the fuzzd web server processes such requests, it fails to implement proper path normalization or validation checks that would prevent access to files outside the intended web root directory. The attacker can traverse the file system hierarchy using multiple directory up commands to reach and retrieve critical system files including but not limited to /etc/passwd, /etc/shadow, and other sensitive configuration files that contain authentication credentials, system information, and potentially system binaries.
The operational impact of this vulnerability extends far beyond simple information disclosure, as it provides attackers with comprehensive access to the device's underlying operating system. Successful exploitation can lead to complete device compromise, allowing attackers to extract authentication credentials, modify system configurations, install malicious software, or establish persistent backdoors. The Maintenance Center interface, which is typically intended for authorized maintenance personnel, becomes a gateway for unauthorized access to the entire device operating system. This vulnerability particularly affects devices deployed in consumer environments where physical security is often limited, making the potential for exploitation more likely. The compromised device can serve as a foothold for further network reconnaissance and lateral movement, especially if the device is connected to larger networks. The vulnerability's impact is amplified by the fact that it affects devices running firmware versions that may be in use for extended periods without updates, leaving organizations vulnerable to exploitation for extended durations.
Mitigation strategies for CVE-2018-7539 should focus on immediate firmware updates provided by the vendor to address the directory traversal vulnerability within the fuzzd web server component. Organizations should implement network segmentation to isolate affected devices from critical network segments, particularly by blocking access to TCP port 8088 from untrusted networks. Network administrators should consider implementing firewall rules to restrict access to the Maintenance Center interface and disable unnecessary services where possible. The vulnerability demonstrates the importance of proper input validation and secure coding practices, particularly when handling user-supplied data in web applications. Security monitoring should include detection of suspicious HTTP request patterns that attempt directory traversal attacks, with the implementation of web application firewalls or intrusion detection systems capable of identifying and blocking such malicious requests. Additionally, organizations should conduct regular vulnerability assessments to identify and remediate similar issues in other networked devices, as this vulnerability type commonly affects embedded systems and IoT devices where security updates may be infrequent or absent. The ATT&CK framework categorizes this vulnerability under T1059 for command and scripting interpreter and T1078 for valid accounts, as exploitation typically involves gaining access through legitimate administrative interfaces and then leveraging the compromised credentials for further system access.