CVE-2021-42071 in DVR VX16
Summary
by MITRE • 10/07/2021
In Visual Tools DVR VX16 4.2.28.0, an unauthenticated attacker can achieve remote command execution via shell metacharacters in the cgi-bin/slogin/login.py Uaer-Agent HTTP header.
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Analysis
by VulDB Data Team • 12/01/2024
The vulnerability identified as CVE-2021-42071 affects Visual Tools DVR VX16 firmware version 4.2.28.0, representing a critical remote code execution flaw that enables unauthenticated attackers to gain system-level control. This vulnerability resides within the web application interface of the digital video recorder device, specifically targeting the cgi-bin/slogin/login.py script that processes user agent headers. The flaw demonstrates characteristics consistent with CWE-74, which describes improper neutralization of special elements used in a command or query, and aligns with ATT&CK technique T1059.007 for command and scripting interpreter. The vulnerability stems from inadequate input validation and sanitization within the user agent header processing mechanism, allowing malicious actors to inject shell metacharacters that are subsequently executed by the underlying system.
The technical exploitation of this vulnerability occurs through manipulation of the User-Agent HTTP header parameter, where an attacker can craft malicious input containing shell command injection sequences. When the vulnerable application processes this header without proper sanitization, the injected commands are executed within the context of the web server process, potentially with elevated privileges depending on the system configuration. This type of vulnerability represents a classic command injection flaw that can be leveraged for arbitrary code execution, data exfiltration, and system compromise. The attack vector is particularly dangerous because it requires no authentication credentials, making it accessible to any remote attacker who can send HTTP requests to the affected device. The vulnerability's impact extends beyond simple command execution to include potential privilege escalation and persistent backdoor establishment.
The operational implications of CVE-2021-42071 are severe for organizations relying on Visual Tools DVR VX16 devices for security monitoring and surveillance. An attacker exploiting this vulnerability can gain complete control over the DVR system, potentially accessing all recorded video footage, modifying system configurations, and using the device as a pivot point for attacks on internal network segments. The device's role as a network security appliance makes this vulnerability particularly concerning, as it can be used to bypass security controls and establish persistent access to monitored environments. The lack of authentication requirements means that this vulnerability can be exploited at scale, potentially affecting multiple devices across different geographical locations without requiring specialized credentials or prior access to the network.
Organizations should implement immediate mitigations including network segmentation to isolate affected devices from critical network segments, deployment of intrusion detection systems to monitor for suspicious User-Agent header patterns, and application-layer firewalls to filter malicious requests. The most effective long-term solution involves updating the firmware to a version that properly sanitizes input parameters and implements proper input validation controls. Security teams should also conduct comprehensive network scans to identify all affected devices and establish monitoring procedures for anomalous command execution patterns. Additionally, implementing principle of least privilege configurations and regular security audits can help reduce the attack surface and limit potential damage from exploitation attempts. The vulnerability underscores the importance of secure coding practices and input validation in embedded web applications, particularly those handling user-supplied data in authentication contexts.