How Hackers Turn DVR Command Injection Flaw into a Botnet Weapon
A new wave of cyberattacks is exploiting a DVR command injection flaw to build a powerful botnet. Security researchers at Fortinet‘s FortiGuard Labs have uncovered a campaign targeting TBK digital video recorders (DVRs). The goal? To install a Mirai-based malware strain called Nexcorium. This malware turns infected devices into soldiers for distributed denial-of-service (DDoS) attacks.
Understanding the DVR Command Injection Flaw (CVE-2024-3721)
The vulnerability at the heart of this campaign is CVE-2024-3721. It affects TBK DVR systems, which are widely used in surveillance setups. Attackers send specially crafted requests to the device, abusing a vulnerable parameter. This allows them to execute arbitrary commands on the system. In short, the DVR command injection flaw gives hackers a direct path into the device.
Once inside, the attackers deploy a downloader script. This script fetches malware binaries tailored for different Linux architectures, including ARM, MIPS, and x86-64. The malware then runs with elevated permissions, taking full control of the DVR.
Inside the Nexcorium Botnet: Multi-Stage Infection and Persistence
Nexcorium is a sophisticated variant of the infamous Mirai botnet. After the initial breach, the malware hides its configuration using XOR encoding. This configuration includes command-and-control (C2) server details, attack instructions, and even a built-in credential list for brute-force attacks.
The botnet spreads through multiple methods. It exploits the DVR command injection flaw for initial access. Then, it uses default credentials to move laterally across networks. It also targets additional vulnerabilities, such as CVE-2017-17215, which affects Huawei routers. This multi-pronged approach helps the botnet grow quickly.
Persistence is a key feature of Nexcorium. The malware modifies system initialization files, creates startup scripts, and registers system services. It also schedules recurring tasks via cron jobs. This ensures the malware survives reboots and maintains long-term access.
DDoS Capabilities of the Botnet
Once established, Nexcorium connects to a remote C2 server. The server issues commands for various DDoS attack methods. These include UDP floods, TCP SYN floods, and application-layer attacks like SMTP flooding. The botnet can also terminate attacks or self-destruct on command, showing centralized control.
As Trey Ford, chief strategy and trust officer at Bugcrowd, noted: “The Nexcorium campaign is a precise illustration of why automated scanning alone cannot close the exposure gap. Machine speed analysis tells you a vulnerability exists, but human researcher depth tells you how an adversary will chain it, weaponize it and sustain access long after the initial alert fires.”
How to Protect IoT Devices from Botnet Threats
IoT devices, especially DVRs, are prime targets for botnets like Nexcorium. John Gallagher, vice president of Viakoo Labs, explained: “Enterprises have had their fleets of IoT and OT devices used by Mirai and its variants for some time, particularly for DDoS attacks. Until more action is taken by enterprises to maintain cyber hygiene on IoT devices, this will continue because of the ease of infection and ability to move laterally.”
Security teams should focus on foundational controls. Traditional agent-based tools often fail because IoT devices cannot host agents. Instead, use agentless discovery and remediation solutions. Automated password and certificate management are also critical. Additionally, keep firmware updated to patch known vulnerabilities like CVE-2024-3721.
For more on IoT security, read our guide on IoT security best practices. You can also check our analysis of Mirai botnet evolution.
In conclusion, the exploitation of the DVR command injection flaw highlights a growing trend: attackers targeting overlooked IoT devices. By understanding the attack chain and implementing strong cyber hygiene, organizations can reduce their risk of becoming part of the next botnet.
