CVE-2018-20305 in DIR-816 A2
Summary
by MITRE
D-Link DIR-816 A2 1.10 B05 devices allow arbitrary remote code execution without authentication via the newpass parameter. In the /goform/form2userconfig.cgi handler function, a long password may lead to a stack-based buffer overflow and overwrite a return address.
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Analysis
by VulDB Data Team • 04/22/2020
The vulnerability identified as CVE-2018-20305 affects D-Link DIR-816 A2 1.10 B05 wireless routers, representing a critical stack-based buffer overflow flaw in the device's web interface handling mechanism. This vulnerability exists within the /goform/form2userconfig.cgi handler function where the newpass parameter is processed without adequate input validation or bounds checking. The flaw allows attackers to execute arbitrary code remotely without requiring authentication credentials, making it particularly dangerous as it bypasses all standard security mechanisms that would normally protect the device's administrative functions.
The technical implementation of this vulnerability stems from improper memory management within the router's firmware where user-supplied password data is directly copied into a fixed-size buffer on the stack without length verification. When an attacker provides an excessively long password string, the data overflows beyond the allocated buffer space, corrupting adjacent memory locations including the return address of the calling function. This memory corruption enables attackers to redirect program execution flow to malicious code injected into the buffer, effectively allowing complete system compromise. The vulnerability falls under CWE-121 Stack-based Buffer Overflow, which is classified as a fundamental memory safety issue that has been consistently exploited in various network device firmware implementations.
The operational impact of this vulnerability extends far beyond simple unauthorized access, as it provides attackers with complete control over the affected router's functionality. Once exploited, attackers can modify network configurations, intercept traffic, create backdoors, or use the device as a pivot point for further attacks within the local network. The lack of authentication requirements means that any remote attacker can exploit this vulnerability, making it particularly dangerous for devices deployed in residential or small office environments where physical security may be lacking. The attack surface is further expanded because routers often serve as the primary gateway for network traffic, providing attackers with potential access to sensitive internal systems and data.
Mitigation strategies for CVE-2018-20305 should prioritize immediate firmware updates from D-Link, as the vendor has released patches addressing this specific vulnerability. Network administrators should implement network segmentation and access controls to limit the potential impact of exploitation, while also monitoring for suspicious network traffic patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1078.004 for Valid Accounts, as exploitation typically involves executing malicious commands through compromised administrative interfaces. Organizations should also consider implementing intrusion detection systems that can identify unusual patterns in requests to the affected CGI handler, particularly those containing unusually long parameter values that could indicate buffer overflow attempts. Regular security audits of network infrastructure and maintaining up-to-date vulnerability assessments are essential to prevent similar issues in other network equipment that may share similar implementation flaws in their authentication and input handling mechanisms.