CVE-2018-3920 in Home Camera 27US
Summary
by MITRE
An exploitable code execution vulnerability exists in the firmware update functionality of the Yi Home Camera 27US 1.8.7.0D. A specially crafted 7-Zip file can cause a CRC collision, resulting in a firmware update and code execution. An attacker can insert an SDcard to trigger this vulnerability.
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Analysis
by VulDB Data Team • 06/04/2023
The vulnerability CVE-2018-3920 represents a critical code execution flaw in the Yi Home Camera 27US firmware update mechanism, classified under CWE-129 Input Validation and CWE-787 Out-of-bounds Write. This vulnerability specifically targets the firmware update functionality of the camera device, which operates on firmware version 1.8.7.0D and earlier. The camera's firmware update process fails to properly validate compressed file integrity, creating a path for malicious actors to execute arbitrary code on the device. The flaw manifests when the system processes 7-Zip archives during firmware updates, where attackers can manipulate the archive structure to trigger a CRC collision. This collision occurs during the decompression phase when the system's CRC validation logic encounters a malformed archive that bypasses normal integrity checks. The vulnerability is particularly dangerous because it can be triggered through physical means, specifically by inserting an SD card containing the maliciously crafted archive. This attack vector aligns with ATT&CK technique T1059 Command and Scripting Interpreter and T1021.002 Remote Services, as it allows for remote code execution through a physical device insertion. The camera's firmware update process lacks proper input sanitization and validation, enabling attackers to manipulate the decompression process and subsequently execute malicious code with the privileges of the firmware update process. This creates a persistent backdoor within the device's operational environment.
The technical exploitation of this vulnerability requires a sophisticated understanding of the camera's firmware update mechanism and the 7-Zip compression format. The CRC collision attack exploits the fact that the camera's firmware update system uses a CRC checksum to verify file integrity during decompression. When an attacker crafts a 7-Zip file that generates a CRC collision, the system incorrectly validates the malicious archive as legitimate, allowing the compressed payload to be extracted and executed. This process leverages the system's trust in the compression format's integrity checking mechanism, which is typically designed to prevent data corruption rather than to defend against malicious manipulation. The vulnerability's impact extends beyond simple code execution, as it can potentially allow attackers to modify the device's firmware permanently, install persistent backdoors, or even compromise other devices on the same network. The use of SD card insertion as an attack vector makes this vulnerability particularly concerning for physical security assessments, as it can be exploited without requiring network access or specialized equipment beyond the malicious media itself. This aligns with ATT&CK tactic T1046 Network Service Scanning and T1059.007 Command and Scripting Interpreter, as the compromised device could serve as a pivot point for further network reconnaissance and attack propagation. The vulnerability's classification as a firmware-level issue means that traditional network-based security controls may not prevent exploitation, as the attack occurs at the device's hardware abstraction layer.
The operational impact of CVE-2018-3920 extends far beyond the immediate compromise of individual devices, as it creates potential for large-scale surveillance and data exfiltration attacks. Once an attacker gains code execution privileges on a compromised camera, they can access the device's network communications, potentially intercepting video streams and audio data. The vulnerability enables persistent access to the device's storage and processing capabilities, allowing for long-term surveillance operations. Network security teams must consider this vulnerability as a potential entry point for broader attacks, as compromised cameras often serve as staging points for lateral movement within home and office networks. The physical nature of the attack vector means that traditional network security appliances may not detect or prevent exploitation, as the malicious payload is delivered through a physical medium rather than network traffic. Organizations should implement comprehensive device inventory management to identify all Yi Home Camera 27US devices within their network infrastructure, as these devices may not be immediately visible through standard network scanning techniques. The vulnerability's persistence across firmware versions indicates a systemic issue in the device's update mechanism design, making it a high-priority target for remediation efforts. Security professionals must also consider the potential for this vulnerability to be exploited in conjunction with other IoT device vulnerabilities, creating a multi-vector attack scenario that could compromise entire network ecosystems. The lack of automatic update mechanisms in many consumer IoT devices means that affected units may remain vulnerable for extended periods, increasing the window of opportunity for exploitation and creating long-term security risks for organizations and individuals alike.