A critical vulnerability in the TP-Link TL-WR940N router has been identified by a security researcher specializing in reverse engineering and exploit development. This vulnerability specifically affects hardware versions 3 and 4, including all firmware up to the latest version. Documented as CVE-2024-54887, this flaw opens the door to potential arbitrary remote code execution (RCE) through stack buffer overflow exploitation.
To uncover this vulnerability, the researcher employed various techniques such as static and dynamic analysis, shellcode development for MIPS Linux, and Return Oriented Programming (ROP) to demonstrate the exploit’s feasibility. By emulating the router’s firmware using Firmadyne, a comprehensive inspection of its functionality was conducted.
During static analysis utilizing tools like Ghidra, it was discovered that key security measures such as Non-Executable (NX) and Position Independent Executables (PIE) were absent. An analysis of the code responsible for processing DNS server settings revealed unbounded calls to strcpy() with the dnsserver1 and dnsserver2 parameters, leaving the system vulnerable to a stack buffer overflow.
With the vulnerability identified, the researcher proceeded to develop an exploit leveraging ROP techniques suitable for the MIPS architecture. This involved creating a series of gadgets to facilitate controlled execution of shellcode for initiating arbitrary commands on the router. Testing confirmed the ability to overwrite critical registers and inject malicious payloads to execute commands on the device.
The final exploit was encapsulated in a Python script capable of authenticating to the router and executing shellcode to establish a bind shell. Subsequent post-exploitation testing verified the exploit’s effectiveness in triggering a bind shell on port 4444 from the compromised device.
Upon communicating the findings to TP-Link, the researcher received acknowledgment of the issue. However, TP-Link clarified that the affected hardware versions had reached their end-of-life status, consequently halting further security updates. As of January 9, 2025, the vulnerability has been officially documented with the assigned CVE number, making a significant contribution to IoT security research.
This discovery underscores the importance of ongoing security assessments for embedded systems, particularly for devices that are still in active use despite the halt of official support. It serves as a reminder of the persistent need for robust security measures to safeguard against potential threats and vulnerabilities in the digital landscape.
The investigation conducted by the security researcher sheds light on the intricate process of identifying, analyzing, and exploiting vulnerabilities in critical network hardware. By leveraging advanced techniques and methodologies, researchers can uncover vulnerabilities that pose significant risks to network security, highlighting the ever-evolving landscape of cybersecurity threats.