CVE-2019-6258 in DIR-822 Rev.Bx
Summary
by MITRE
D-Link DIR-822 Rev.Bx devices with firmware v.202KRb06 and older allow a buffer overflow via long MacAddress data in a /HNAP1/SetClientInfo HNAP protocol message, which is mishandled in /usr/sbin/udhcpd during reading of the /var/servd/LAN-1-udhcpd.conf file.
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Analysis
by VulDB Data Team • 11/10/2020
The vulnerability CVE-2019-6258 affects D-Link DIR-822 Rev.Bx wireless routers running firmware versions v.202KRb06 and earlier, representing a critical buffer overflow flaw within the device's network management protocols. This vulnerability specifically targets the HNAP (Home Network Application Protocol) implementation, which serves as the primary interface for device configuration and management through HTTP requests. The flaw manifests when the system processes a maliciously crafted SetClientInfo request containing excessively long MacAddress data, creating conditions for memory corruption that can be exploited by remote attackers.
The technical execution of this vulnerability occurs within the udhcpd daemon, which operates in the /usr/sbin/udhcpd binary and handles DHCP configuration file processing. During the reading of /var/servd/LAN-1-udhcpd.conf, the system fails to properly validate input length before copying data into fixed-size buffers, resulting in a classic stack-based buffer overflow condition. This flaw falls under CWE-121, stack-based buffer overflow, and specifically demonstrates the dangerous practice of using unsafe string handling functions without proper bounds checking. The overflow occurs in the context of a network service daemon, making it particularly dangerous as it can be triggered through unauthenticated network requests.
The operational impact of this vulnerability extends beyond simple denial of service, as it creates potential for remote code execution on affected devices. Attackers can leverage this buffer overflow to overwrite critical memory locations, potentially allowing them to execute arbitrary code with the privileges of the udhcpd process, which typically runs with elevated system permissions. This creates a significant risk for network compromise, as the attacker could gain persistent access to the router's network management functions and potentially use the device as a pivot point for attacking other systems within the local network. The vulnerability affects the device's ability to maintain network connectivity and configuration integrity, making it particularly concerning for enterprise and residential network security.
Mitigation strategies for CVE-2019-6258 should prioritize immediate firmware updates from D-Link to address the underlying buffer overflow conditions in the udhcpd implementation. Network administrators should also implement network segmentation and access controls to limit exposure of affected devices to untrusted networks. The vulnerability demonstrates the importance of secure coding practices and input validation in network services, aligning with ATT&CK technique T1059.007 for command and scripting interpreter execution through network protocols. Additional defensive measures include monitoring for unusual HNAP protocol traffic patterns and implementing network intrusion detection systems to identify potential exploitation attempts. Organizations should also consider disabling unnecessary network services and applying network-level restrictions to prevent unauthorized access to the device management interfaces.