CVE-2018-8941 in DSL-3782
Summary
by MITRE
Diagnostics functionality on D-Link DSL-3782 devices with firmware EU v. 1.01 has a buffer overflow, allowing authenticated remote attackers to execute arbitrary code via a long Addr value to the 'set Diagnostics_Entry' function in an HTTP request, related to /userfs/bin/tcapi.
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Analysis
by VulDB Data Team • 01/21/2020
The vulnerability identified as CVE-2018-8941 affects D-Link DSL-3782 broadband routers running firmware version EU v. 1.01 and potentially other affected models. This represents a critical security flaw within the device's diagnostic subsystem that enables authenticated remote code execution through a carefully crafted buffer overflow attack. The vulnerability specifically targets the tcapi binary located in the /userfs/bin/ directory, which serves as the core component for handling diagnostic entries within the router's web interface. The attack vector involves sending an HTTP request containing an excessively long Addr parameter to the set Diagnostics_Entry function, which triggers the buffer overflow condition in the underlying software implementation.
The technical flaw stems from inadequate input validation within the diagnostic functionality of the router's web server implementation. When the system processes the maliciously crafted Addr parameter, it fails to properly bounds-check the input length before copying it into a fixed-size buffer. This classic buffer overflow vulnerability falls under CWE-121, which specifically addresses stack-based buffer overflow conditions. The vulnerability allows an attacker who has already established authentication credentials to the device to escalate privileges and execute arbitrary code with the highest possible privileges available to the diagnostic service. The tcapi binary typically runs with elevated privileges to perform system-level diagnostic operations, making this attack particularly dangerous as it could enable full system compromise.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with complete control over the affected router. Once exploited, the attacker gains the ability to modify network configurations, redirect traffic, install malicious firmware, or use the device as a pivot point for attacking other systems within the local network. The vulnerability affects the router's core networking functionality, potentially allowing attackers to disrupt network services, monitor traffic, or establish persistent backdoors. From an attacker's perspective, this vulnerability represents a significant advantage since it requires only authentication credentials, which are often weak or default passwords. The attack can be executed remotely over the internet, making it particularly dangerous for devices with exposed management interfaces.
Security mitigation strategies for this vulnerability involve multiple layers of protection including immediate firmware updates from D-Link to address the buffer overflow condition, network segmentation to limit access to router management interfaces, and strict access control policies for administrative accounts. Organizations should implement strong authentication mechanisms including multi-factor authentication and regular password changes to reduce the risk of unauthorized access. Network monitoring should be enhanced to detect unusual traffic patterns or attempts to access diagnostic functions. The ATT&CK framework categorizes this vulnerability under T1059 for command and scripting interpreter and T1068 for exploit for privilege escalation, highlighting the need for both network-level defenses and endpoint protection measures. Regular vulnerability assessments and security audits should be conducted to identify similar buffer overflow conditions in other network infrastructure components. Given the nature of the vulnerability, it is recommended that affected devices be taken offline until proper patches are applied and that network administrators implement strict firewall rules to restrict access to router management interfaces from untrusted networks.