CVE-2018-19987 in DIR-822
Summary
by MITRE
D-Link DIR-822 Rev.B 202KRb06, DIR-822 Rev.C 3.10B06, DIR-860L Rev.B 2.03.B03, DIR-868L Rev.B 2.05B02, DIR-880L Rev.A 1.20B01_01_i3se_BETA, and DIR-890L Rev.A 1.21B02_BETA devices mishandle IsAccessPoint in /HNAP1/SetAccessPointMode. In the SetAccessPointMode.php source code, the IsAccessPoint parameter is saved in the ShellPath script file without any regex checking. After the script file is executed, the command injection occurs. A vulnerable /HNAP1/SetAccessPointMode XML message could have shell metacharacters in the IsAccessPoint element such as the `telnetd` string.
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Analysis
by VulDB Data Team • 09/15/2023
This vulnerability exists in multiple D-Link router models including DIR-822, DIR-860L, DIR-868L, DIR-880L, and DIR-890L devices running specific firmware versions. The flaw resides in the HNAP1/SetAccessPointMode endpoint where the IsAccessPoint parameter is improperly handled during script file generation. The vulnerability stems from insufficient input validation and sanitization mechanisms within the SetAccessPointMode.php source code, which directly incorporates user-supplied data into shell command execution without proper filtering or escaping. This represents a classic command injection vulnerability that allows remote attackers to execute arbitrary shell commands on the affected devices.
The technical implementation of this vulnerability occurs through the manipulation of the IsAccessPoint parameter within the XML message structure sent to the HNAP1/SetAccessPointMode endpoint. When the system processes this parameter, it stores the value directly into a ShellPath script file without any regular expression validation or input sanitization. Once the script file is executed, the unsanitized input gets interpreted as shell commands, creating a command injection vector. Attackers can leverage this by embedding shell metacharacters such as the `telnetd` string within the IsAccessPoint element, which then gets executed with the privileges of the web server process. This vulnerability is particularly dangerous because it operates at the system level and can be exploited remotely without authentication.
The operational impact of this vulnerability is severe and multifaceted. Remote attackers can execute arbitrary commands on affected devices, potentially gaining full control over the router's functionality. This includes the ability to establish persistent backdoors, modify network configurations, redirect traffic, and compromise the entire network infrastructure. The vulnerability affects multiple device models across different firmware versions, indicating a widespread issue within the D-Link product line. The lack of input validation creates a persistent threat vector that can be exploited by attackers with minimal technical expertise, as demonstrated by the inclusion of common shell metacharacters in the exploit payload. This vulnerability directly aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and maps to ATT&CK technique T1059.001 for command and scripting interpreter.
The security implications extend beyond simple command execution to encompass complete network compromise. An attacker who successfully exploits this vulnerability can gain unauthorized access to the router's administrative interface, modify firewall rules, change DNS settings, and potentially use the compromised device as a pivot point for attacking internal network systems. The vulnerability's persistence is enhanced by the fact that it operates through the HNAP protocol, which is commonly used for device management and configuration, making it less likely to be detected by network monitoring systems. Organizations should consider implementing network segmentation and monitoring for unusual HNAP traffic patterns to detect potential exploitation attempts. Immediate mitigation strategies include firmware updates from D-Link, network access control measures, and disabling unnecessary HNAP services when not required for legitimate operations. The vulnerability demonstrates the critical importance of input validation and proper sanitization of user-supplied data in web applications and network device management interfaces.