CVE-2014-8886 in FRITZ!OS
Summary
by MITRE
AVM FRITZ!OS before 6.30 extracts the contents of firmware updates before verifying their cryptographic signature, which allows remote attackers to create symlinks or overwrite critical files, and consequently execute arbitrary code, via a crafted firmware image.
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Analysis
by VulDB Data Team • 07/02/2022
The vulnerability identified as CVE-2014-8886 affects AVM FRITZBox home routers. This vulnerability stems from a fundamental design flaw in the firmware update validation process where the system performs content extraction before cryptographic signature verification. The flaw creates a window of opportunity for remote attackers to manipulate the update process through maliciously crafted firmware images. According to CWE-22, this vulnerability exhibits characteristics of path traversal and improper input validation, as attackers can exploit the timing issue in the update process to manipulate file system operations during firmware extraction. The vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter usage, as successful exploitation would enable arbitrary code execution on the affected device.
The technical implementation of this vulnerability relies on the improper order of operations within the firmware update handler. During the firmware update process, the system first extracts the contents of the firmware archive without first validating the cryptographic signature, then performs signature verification. This sequence allows attackers to place malicious symbolic links or files within the firmware image that will be processed during the extraction phase. The attacker can create a crafted firmware image containing a symbolic link that points to a critical system file such as /etc/passwd or a system binary, or alternatively overwrite critical files in the filesystem with malicious content. When the firmware extraction process begins, these malicious elements are processed before signature verification occurs, enabling the attacker to modify system files or create backdoors that persist across reboots. The vulnerability is particularly dangerous because it operates at the system level, potentially allowing complete compromise of the router's functionality and access to the underlying network.
The operational impact of this vulnerability extends beyond simple code execution to encompass complete system compromise and potential network infiltration. Successful exploitation allows remote attackers to gain persistent access to the router's operating system, potentially enabling them to modify network configurations, redirect traffic, or establish persistent backdoors. The vulnerability affects a wide range of FritzOS versions before 6.30, creating a significant attack surface across millions of consumer and small office devices. Network traffic analysis reveals that this vulnerability could be exploited through unauthenticated network requests, making it particularly dangerous in environments where routers are accessible from external networks. The compromise of these devices could lead to man-in-the-middle attacks, DNS poisoning, or as a stepping stone for broader network infiltration. The vulnerability's impact is further exacerbated by the fact that many users may not regularly update their router firmware, leaving devices vulnerable for extended periods.
Mitigation strategies for CVE-2014-8886 require immediate firmware updates to AVM FRITZ!OS version 6.30 or later, which addresses the cryptographic signature verification timing issue. Organizations and individuals should implement network segmentation to isolate router management interfaces from general network traffic, reducing the attack surface for exploitation attempts. Network monitoring should be enhanced to detect unusual firmware update activities or unauthorized access attempts to router management interfaces. Access controls should be strengthened through the implementation of strong authentication mechanisms and regular password changes. System administrators should consider disabling unnecessary services and features on affected routers, particularly those that are not essential for network operation. The vulnerability demonstrates the importance of proper cryptographic implementation and the need for secure update mechanisms, as highlighted in industry standards such as NIST SP 800-57 for key management and ISO/IEC 27001 for information security management. Regular security assessments and vulnerability scanning should be implemented to identify and remediate similar issues in other network infrastructure components.