CVE-2014-9727 in FRITZ!Box
Summary
by MITRE
AVM Fritz!Box allows remote attackers to execute arbitrary commands via shell metacharacters in the var:lang parameter to cgi-bin/webcm.
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Analysis
by VulDB Data Team • 08/25/2024
The CVE-2014-9727 vulnerability represents a critical command injection flaw in AVM FritzBox series devices, specifically in the cgi-bin/webcm script that handles various administrative functions. The issue stems from insufficient input validation and sanitization of user-supplied parameters, particularly the var:lang parameter that is used to determine the language of the web interface. Attackers can exploit this weakness by injecting shell metacharacters directly into the var:lang parameter, which then gets processed by the underlying shell without proper sanitization, creating a direct path for arbitrary command execution.
This vulnerability operates at the intersection of multiple security concerns including CWE-77 and CWE-94, which respectively address improper neutralization of special elements used in command execution and weaknesses in web applications that allow arbitrary code execution. The attack vector is particularly dangerous because it leverages the web management interface, which typically runs with elevated privileges and has direct access to the underlying operating system. The exploitation process involves crafting malicious input containing shell metacharacters such as semicolons, ampersands, or backticks that get interpreted by the system shell, enabling attackers to execute arbitrary commands with the privileges of the web server process. This represents a classic command injection vulnerability that can be classified under the ATT&CK technique T1059.001 for command and scripting interpreter.
The operational impact of CVE-2014-9727 extends far beyond simple remote code execution, as it provides attackers with complete control over the affected router. Once exploited, adversaries can access the entire network infrastructure, modify firewall rules, install malicious software, redirect traffic, or even use the device as a pivot point for further attacks against internal network systems. The vulnerability affects a wide range of FritzBox 7390, 7490, 7530, and 7590 series, making it particularly dangerous as these devices are commonly deployed in residential and small office environments where network security is often inadequate. The remote nature of the attack means that no physical access or local network presence is required, allowing attackers to compromise devices from anywhere on the internet, which significantly increases the attack surface and potential impact.
Mitigation strategies for CVE-2014-9727 should include immediate firmware updates from AVM, which addressed the vulnerability by implementing proper input validation and sanitization for all user-supplied parameters. Network administrators should also consider implementing network segmentation to limit the impact of potential compromises, disable remote management features when not actively needed, and monitor network traffic for suspicious patterns that might indicate exploitation attempts. Additional security measures include implementing web application firewalls to detect and block malicious payloads targeting the cgi-bin/webcm endpoint, restricting access to the web management interface to specific IP addresses, and regularly auditing device configurations. The vulnerability highlights the importance of input validation in web applications and serves as a reminder of the critical security risks associated with embedded devices that are frequently overlooked in security assessments. Organizations should also consider implementing network monitoring solutions that can detect unusual command execution patterns and provide real-time alerts for potential exploitation attempts.