CVE-2018-18754 in VMG3312-B10B
Summary
by MITRE
ZyXEL VMG3312-B10B 1.00(AAPP.7) devices have a backdoor root account with the tTn3+Z@!Sr0O+ password hash in the etc/default.cfg file.
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Analysis
by VulDB Data Team • 04/07/2020
The vulnerability identified as CVE-2018-18754 represents a critical security flaw in ZyXEL VMG3312-B10B broadband routers running firmware version 1.00(AAPP.7). This issue manifests through the presence of a hardcoded backdoor account within the device configuration file, specifically located at etc/default.cfg. The backdoor account contains a predictable password hash that allows unauthorized access to the device with root privileges, effectively bypassing all normal authentication mechanisms. This vulnerability directly violates fundamental security principles by providing persistent unauthorized access paths that remain active regardless of user configuration changes or security updates.
The technical implementation of this backdoor follows a pattern commonly associated with CWE-798, which addresses the use of hard-coded credentials in software systems. The vulnerability exploits the insecure storage of authentication credentials by embedding a password hash directly within the device's default configuration file, making it accessible to anyone who can read the file or has physical access to the device. The specific password hash tTn3+Z@!Sr0O+ represents a weak cryptographic implementation that can be easily reverse-engineered or brute-forced, particularly given the predictable nature of such backdoor implementations. This flaw demonstrates poor security engineering practices and violates the principle of least privilege by providing unrestricted administrative access to unauthorized parties.
The operational impact of this vulnerability is severe and multifaceted across multiple security domains. Attackers can leverage this backdoor to establish persistent access to network infrastructure, potentially enabling them to modify device configurations, intercept network traffic, or use the device as a pivot point for attacking other systems within the network. The presence of such a backdoor undermines the integrity of the entire network security posture, as it provides an always-available entry point that bypasses all normal security controls including firewalls, intrusion detection systems, and network segmentation measures. This vulnerability aligns with ATT&CK technique T1078.004, which covers legitimate credentials, and T1566.001, representing spearphishing with a backdoor, as the backdoor account essentially provides a persistent foothold for attackers.
Organizations and network administrators should immediately implement comprehensive mitigation strategies to address this vulnerability. The primary recommendation involves replacing affected devices with firmware versions that have removed the backdoor account and implemented proper credential management practices. Network segmentation should be enhanced to limit the potential impact of compromised devices, while monitoring systems should be configured to detect unusual network activity that might indicate unauthorized access. Additionally, security audits should include verification of device configuration files to ensure no unauthorized accounts or credentials remain. The vulnerability highlights the importance of supply chain security and the necessity of conducting thorough security assessments of all network infrastructure components, particularly those from vendors with known security vulnerabilities. This issue also underscores the critical need for regular firmware updates and the implementation of robust change management processes to prevent unauthorized modifications to network device configurations.