CVE-2018-8879 in Asuswrt-Merlin
Summary
by MITRE
Stack-based buffer overflow in Asuswrt-Merlin firmware for ASUS devices older than 384.4 and ASUS firmware before 3.0.0.4.382.50470 for devices allows remote attackers to execute arbitrary code by providing a long string to the blocking.asp page via a GET or POST request. Vulnerable parameters are flag, mac, and cat_id.
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Analysis
by VulDB Data Team • 02/26/2024
The vulnerability identified as CVE-2018-8879 represents a critical stack-based buffer overflow flaw in the Asuswrt-Merlin firmware ecosystem affecting ASUS networking devices. This vulnerability exists within the blocking.asp web page component that handles incoming HTTP requests from remote attackers. The flaw manifests when the firmware fails to properly validate input lengths for specific parameters, creating a condition where maliciously crafted payloads can overflow the allocated stack memory space. The affected versions include ASUS devices running firmware versions prior to 384.4 for Asuswrt-Merlin and firmware versions before 3.0.0.4.382.50470 for standard ASUS firmware implementations. The vulnerability specifically targets three parameters: flag, mac, and cat_id which are processed through GET or POST HTTP methods, making it accessible via various network interaction vectors.
The technical exploitation of this vulnerability occurs through a well-defined attack pattern that leverages the fundamental flaw in input validation mechanisms. When an attacker submits a maliciously long string to any of the three vulnerable parameters through the blocking.asp page, the firmware's insufficient bounds checking allows the input data to exceed the allocated stack buffer capacity. This overflow condition creates an opportunity for arbitrary code execution within the device's operating environment, as the overflow can overwrite adjacent memory locations including return addresses and control flow information. The stack-based nature of this vulnerability means that the memory corruption directly affects the program's execution stack, potentially allowing attackers to redirect program execution to malicious code payloads. This vulnerability aligns with CWE-121 stack-based buffer overflow classification and represents a classic example of unsafe string handling in embedded network device firmware.
The operational impact of CVE-2018-8879 extends beyond simple remote code execution to encompass significant network security implications for affected ASUS devices. Once successfully exploited, attackers can gain full control over the device's operating system, potentially enabling them to modify network configurations, establish persistent backdoors, intercept network traffic, or use the compromised device as a pivot point for further network reconnaissance and attacks. The remote nature of this vulnerability means that attackers do not require physical access to the device, making it particularly dangerous for enterprise and home network environments. Devices running vulnerable firmware become potential entry points for broader network attacks, as they can be used to launch attacks against other networked systems or to create persistent access points for future exploitation attempts. The vulnerability affects a wide range of ASUS networking equipment including routers and access points, making it a significant concern for network administrators managing multiple devices.
Mitigation strategies for CVE-2018-8879 focus primarily on firmware updates and network-level protections. The most effective immediate solution involves upgrading affected ASUS devices to firmware versions that contain patches for this vulnerability, specifically versions 384.4 for Asuswrt-Merlin and 3.0.0.4.382.50470 or later for standard ASUS firmware. Network administrators should implement network segmentation and monitoring to detect suspicious traffic patterns that might indicate exploitation attempts. Additional protective measures include disabling unnecessary web interfaces, implementing strict access controls for administrative interfaces, and deploying intrusion detection systems that can identify malformed requests targeting the vulnerable blocking.asp page. From an ATT&CK framework perspective, this vulnerability maps to techniques involving remote code execution and privilege escalation, with potential for lateral movement once initial compromise occurs. The vulnerability also demonstrates the importance of input validation and secure coding practices in embedded systems, as highlighted by the need for proper bounds checking in firmware implementations. Organizations should conduct comprehensive vulnerability assessments to identify all potentially affected devices within their network infrastructure and ensure timely patch deployment across all affected systems.