CVE-2018-20056 in DIR-605L
Summary
by MITRE
An issue was discovered in /bin/boa on D-Link DIR-619L Rev.B 2.06B1 and DIR-605L Rev.B 2.12B1 devices. There is a stack-based buffer overflow allowing remote attackers to execute arbitrary code without authentication via the goform/formLanguageChange currTime parameter.
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Analysis
by VulDB Data Team • 04/19/2020
The vulnerability identified as CVE-2018-20056 represents a critical stack-based buffer overflow flaw within the web interface of D-Link wireless routers, specifically affecting models DIR-619L Rev.B 2.06B1 and DIR-605L Rev.B 2.12B1. This issue resides in the /bin/boa binary which serves as the web server component for these devices, making it a prime target for remote exploitation. The vulnerability manifests through the goform/formLanguageChange endpoint where the currTime parameter fails to properly validate input length, creating an exploitable condition that allows attackers to overwrite adjacent stack memory regions.
The technical implementation of this vulnerability follows the classic stack-based buffer overflow pattern where insufficient bounds checking permits an attacker to inject malicious data exceeding the allocated buffer space. When the currTime parameter is processed by the vulnerable web server, the input is directly copied to a fixed-size stack buffer without proper length validation or sanitization. This allows an attacker to craft a specially formatted request containing excessive data that overflows the buffer and corrupts adjacent memory locations including return addresses and control data. The lack of authentication requirements means that any remote attacker can exploit this vulnerability without requiring valid credentials, significantly increasing the attack surface and potential impact.
From an operational perspective, this vulnerability presents a severe risk to network security as it enables remote code execution on affected devices with full administrative privileges. Successful exploitation allows attackers to gain complete control over the router's functionality, potentially enabling them to modify network configurations, install malicious firmware, redirect traffic, or establish persistent backdoors for future access. The impact extends beyond individual device compromise as compromised routers can serve as launching points for broader network attacks, lateral movement, or as part of botnet operations. Network administrators face the challenge of identifying vulnerable devices within their infrastructure without direct access to the affected models, as the vulnerability exists in the device's web interface and can be exploited from external networks.
The vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflow conditions where data is copied to a stack buffer without proper bounds checking. From an ATT&CK framework perspective, this represents a technique for privilege escalation and persistence, as the vulnerability allows for remote code execution without authentication requirements. The lack of authentication requirements places this vulnerability in the category of techniques that enable initial access without user interaction, making it particularly dangerous for network infrastructure devices. Mitigation strategies should include immediate firmware updates from D-Link, network segmentation to limit access to affected devices, and implementing network monitoring to detect exploitation attempts. Additionally, organizations should consider disabling unnecessary web interfaces on network devices and implementing proper access controls to reduce the attack surface. The vulnerability demonstrates the importance of proper input validation and secure coding practices, particularly in embedded systems where resource constraints may lead to insufficient security measures.