CVE-2018-19986 in DIR-818LW
Summary
by MITRE
In the /HNAP1/SetRouterSettings message, the RemotePort parameter is vulnerable, and the vulnerability affects D-Link DIR-818LW Rev.A 2.05.B03 and DIR-822 B1 202KRb06 devices. In the SetRouterSettings.php source code, the RemotePort parameter is saved in the $path_inf_wan1."/web" internal configuration memory without any regex checking. And in the IPTWAN_build_command function of the iptwan.php source code, the data in $path_inf_wan1."/web" is used with the iptables command without any regex checking. A vulnerable /HNAP1/SetRouterSettings XML message could have shell metacharacters in the RemotePort element such as the `telnetd` string.
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Analysis
by VulDB Data Team • 09/15/2023
The vulnerability described in CVE-2018-19986 represents a critical command injection flaw within D-Link router firmware versions DIR-818LW Rev.A 2.05.B03 and DIR-822 B1 202KRb06. This vulnerability exists in the HNAP1 web service interface implementation where the RemotePort parameter is processed without proper input validation or sanitization. The flaw stems from the absence of regex validation when handling user-supplied data in the SetRouterSettings.php script, which directly stores the RemotePort value into internal configuration memory at $path_inf_wan1."/web". This unvalidated data subsequently flows into the IPTWAN_build_command function within iptwan.php without any additional sanitization measures. The vulnerability manifests when an attacker crafts a malicious XML message containing shell metacharacters within the RemotePort element, specifically targeting strings like `telnetd` that could enable remote command execution. This represents a classic command injection vulnerability categorized under CWE-77, where user-controllable input is directly incorporated into system commands without proper validation or escaping mechanisms.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass full system compromise and persistent remote access capabilities. Attackers can leverage this flaw to execute arbitrary shell commands on the affected routers, potentially leading to complete network infiltration and lateral movement within the compromised network infrastructure. The vulnerability affects the core networking functionality of these devices, as the RemotePort parameter is typically used for configuring port forwarding rules, making it a prime target for exploitation. The lack of input validation creates a persistent threat vector that remains active as long as the vulnerable firmware version is in use, particularly concerning devices deployed in residential or small business environments where firmware updates may be infrequent. The vulnerability also aligns with ATT&CK technique T1059.001 for command and scripting interpreter, where adversaries use shell commands to establish persistence and execute malicious operations on compromised systems.
Mitigation strategies for CVE-2018-19986 require immediate firmware updates from D-Link to address the input validation deficiencies in the HNAP1 service implementation. Network administrators should implement network segmentation and firewall rules to restrict access to the HNAP1 interface from untrusted networks, as this service typically operates on port 80 or 443 and is accessible via HTTP requests. Additionally, implementing web application firewalls and input validation rules can help detect and prevent malicious XML payloads containing shell metacharacters. The vulnerability demonstrates the importance of proper input sanitization and the principle of least privilege in embedded system security, where parameters should be validated against expected value ranges and patterns before being processed. Organizations should also consider disabling unnecessary web services and remote management features on network devices, as this vulnerability could be exploited through various attack vectors including web-based exploitation and potentially through compromised management interfaces. Regular security assessments and firmware update policies are essential to prevent exploitation of similar vulnerabilities in other network infrastructure components.