CVE-2018-17787 in DIR-823G
Summary
by MITRE
On D-Link DIR-823G devices, the GoAhead configuration allows /HNAP1 Command Injection via shell metacharacters in the POST data, because this data is sent directly to the "system" library function.
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Analysis
by VulDB Data Team • 03/29/2020
The vulnerability CVE-2018-17787 affects D-Link DIR-823G wireless routers and represents a critical command injection flaw within the device's web interface. This issue resides in the GoAhead web server implementation that handles HTTP requests for the router's administrative functions. The vulnerability stems from improper input validation and sanitization within the HNAP1 (Home Network Access Protocol) interface, which is used for remote management of the device. When administrators or attackers submit POST data through the web interface, the system fails to properly sanitize the input before executing system commands, creating a direct pathway for arbitrary code execution.
The technical implementation of this vulnerability occurs at the application level where user-supplied data is directly passed to the system library function without adequate sanitization or validation. This type of flaw falls under CWE-77, which specifically addresses command injection vulnerabilities in software applications. The vulnerability exists because the GoAhead web server component does not properly escape or filter special shell metacharacters such as semicolons, ampersands, or backticks that could be used to chain commands. When these characters are present in the POST data, they are interpreted by the underlying shell and executed as part of the command sequence, allowing attackers to execute arbitrary system commands with the privileges of the web server process.
The operational impact of this vulnerability is severe as it provides attackers with complete control over the affected router. An attacker who can submit malicious POST data to the HNAP1 endpoint can execute arbitrary commands on the device, potentially leading to full system compromise. This includes the ability to modify router configurations, install malware, create backdoors, or use the device as a pivot point for attacking other systems on the local network. The vulnerability affects the device's administrative interface, which typically runs with elevated privileges, making the attack surface particularly dangerous. Network intruders could exploit this vulnerability to gain persistent access to the router and potentially compromise all devices connected to the network.
Mitigation strategies for this vulnerability should focus on both immediate remediation and long-term security improvements. The most effective immediate solution is to update the firmware to a version that properly sanitizes input before passing it to system functions, which D-Link has addressed in subsequent releases. Organizations should also implement network segmentation to limit access to administrative interfaces, restrict access to the router's web interface to trusted IP addresses only, and disable unnecessary services. From a defensive perspective, this vulnerability aligns with ATT&CK technique T1059.001 for command and scripting interpreter, and T1078 for valid accounts, as attackers can leverage legitimate administrative interfaces to execute malicious commands. Regular security assessments and input validation testing should be implemented to prevent similar issues in other network devices, particularly those implementing web-based management interfaces with direct system command execution capabilities.