CVE-2019-18852 in DIR-600
Summary
by MITRE
Certain D-Link devices have a hardcoded Alphanetworks user account with TELNET access because of /etc/config/image_sign or /etc/alpha_config/image_sign. This affects DIR-600 B1 V2.01 for WW, DIR-890L A1 v1.03, DIR-615 J1 v100 (for DCN), DIR-645 A1 v1.03, DIR-815 A1 v1.01, DIR-823 A1 v1.01, and DIR-842 C1 v3.00.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 02/11/2024
The vulnerability identified as CVE-2019-18852 represents a critical security flaw affecting multiple D-Link wireless routers and access points. This issue stems from the presence of a hardcoded administrative account within the device firmware, specifically designed to facilitate remote management through TELNET protocol access. The vulnerability manifests in the configuration files located at /etc/config/image_sign or /etc/alpha_config/image_sign, which contain persistent credentials that remain unchanged across device deployments. This hardcoded account poses a significant risk to network security as it provides unauthorized access to devices that should remain protected from external exploitation attempts.
The technical implementation of this flaw involves the inclusion of a default username and password combination within the device firmware image itself. This practice violates fundamental security principles and creates a persistent backdoor that remains active regardless of user configuration changes. The affected devices include several models from D-Link's DIR-600, DIR-890L, DIR-615, DIR-645, DIR-815, DIR-823, and DIR-842 series, all of which share this common vulnerability in their respective firmware versions. The TELNET access mechanism is particularly concerning because it operates without encryption, making credentials susceptible to interception during transmission. This vulnerability directly maps to CWE-798, which addresses the use of hard-coded credentials, and aligns with ATT&CK technique T1078.004, focusing on legitimate credentials for unauthorized access.
The operational impact of this vulnerability extends far beyond simple unauthorized access, as it enables attackers to gain complete administrative control over affected devices. Once compromised, adversaries can modify network configurations, redirect traffic, install malicious firmware, or establish persistent access points within the network infrastructure. The presence of TELNET access without proper authentication mechanisms creates a vector for lateral movement within networks, allowing attackers to use these devices as entry points for broader attacks. Network administrators face significant challenges in detecting this vulnerability since the hardcoded credentials remain active even after device reboots or configuration resets. The affected firmware versions suggest this flaw existed for extended periods, potentially allowing attackers to exploit it for years without detection.
Mitigation strategies for this vulnerability require immediate firmware updates from D-Link to address the hardcoded credentials issue. Organizations should conduct comprehensive network scans to identify all affected devices and implement network segmentation to limit potential damage from compromised routers. The recommended approach includes disabling TELNET access and enabling SSH alternatives where available, while also enforcing strict access controls for network management interfaces. Security teams must also implement continuous monitoring for unauthorized network access patterns and establish protocols for firmware update management across all network infrastructure components. The vulnerability highlights the importance of secure development practices and the necessity of removing hardcoded credentials from production firmware images. Additionally, network administrators should consider implementing intrusion detection systems specifically designed to identify unauthorized TELNET connections and credential harvesting attempts that may indicate exploitation of this vulnerability.