CVE-2015-6949 in TM-AC1900 Router
Summary
by MITRE
Stack-based buffer overflow in the ASUS TM-AC1900 router allows remote attackers to execute arbitrary code via crafted HTTP header values.
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Analysis
by VulDB Data Team • 06/15/2022
The CVE-2015-6949 vulnerability represents a critical stack-based buffer overflow flaw discovered in the ASUS TM-AC1900 wireless router firmware, which exposes a significant security weakness in network infrastructure devices. This vulnerability resides within the router's web interface handling mechanism, specifically in how it processes HTTP header values during web requests. The flaw manifests when the router's firmware fails to properly validate the length of incoming HTTP headers, allowing an attacker to craft malicious header values that exceed the allocated stack buffer space. This condition creates an exploitable memory corruption scenario that can be leveraged for remote code execution without requiring any authentication or physical access to the device. The vulnerability affects the router's HTTP server component, which is responsible for handling web-based management requests from administrators and users, making it a prime target for attackers seeking persistent access to network environments.
The technical exploitation of this vulnerability follows a classic stack buffer overflow attack pattern where attacker-controlled data is written beyond the bounds of a fixed-length buffer allocated on the program stack. In the context of the ASUS TM-AC1900, this occurs when HTTP headers containing specially crafted payloads are sent to the router's web server, causing the buffer overflow to overwrite adjacent stack memory locations including return addresses and function pointers. This memory corruption enables attackers to redirect program execution flow and inject malicious code that can be executed with the privileges of the web server process. The vulnerability's remote nature means that attackers can exploit it from any location on the internet without requiring local network access, making it particularly dangerous for network administrators who may not be aware of the device's exposure. According to CWE classification, this vulnerability maps to CWE-121 Stack-based Buffer Overflow, which is categorized under the broader weakness of buffer overflow conditions that can lead to arbitrary code execution.
The operational impact of CVE-2015-6949 extends far beyond simple remote code execution, as it fundamentally compromises the security posture of any network environment where affected routers are deployed. Once exploited, attackers can gain complete control over the router's functionality, enabling them to modify network settings, redirect traffic through malicious proxies, establish backdoor access points, or use the device as a launching platform for further attacks against internal network resources. The vulnerability creates a persistent threat vector that can remain active even after the initial compromise, as the attacker can maintain access through the compromised router's management interface. This makes the vulnerability particularly concerning for enterprise networks, small business environments, and home users who may not regularly update their router firmware. The attack surface is further expanded because routers typically operate with elevated privileges and have direct access to network traffic, making them ideal targets for attackers seeking to establish long-term network infiltration. This aligns with ATT&CK technique T1071.004 for application layer protocol usage and T1059.007 for command and scripting interpreter for remote code execution.
Mitigation strategies for CVE-2015-6949 require immediate action from network administrators to address the vulnerability through firmware updates provided by ASUS, as well as network-level defensive measures. The primary solution involves applying the official firmware patch released by ASUS that corrects the buffer overflow condition in the HTTP header processing code, which should be implemented as a priority across all affected devices. Network administrators should also consider implementing network segmentation to limit the potential impact of a successful exploitation, ensuring that even if one router is compromised, the attacker's access remains restricted to a specific network segment. Additional defensive measures include monitoring network traffic for suspicious HTTP header patterns, implementing web application firewalls to detect and block malformed requests, and conducting regular vulnerability assessments to identify other potentially affected network devices. Organizations should also establish firmware update policies that ensure all network infrastructure devices receive timely security patches, as this vulnerability demonstrates how outdated firmware can leave critical network assets exposed to remote exploitation. The vulnerability underscores the importance of maintaining up-to-date network device firmware and implementing robust security monitoring practices to detect and respond to such threats before they can be successfully exploited.