Threat actors are exploiting security flaws in TBK DVR and end-of-life (EoL) TP-Link Wi-Fi routers to deploy Mirai-botnet variants on compromised devices, according to findings from Fortinet FortiGuard Labs and Palo Alto Networks Unit 42. The attack targeting TBK DVR devices has been found to exploit CVE-2024-3721 (CVSS score: 6.3), a medium-severity command injection vulnerability affecting TBK DVR-4104 and DVR-4216 digital video recording devices, to deliver a Mirai variant called Nexcorium.
“IoT devices are increasingly prime targets for large-scale attacks due to their widespread use, lack of patching, and often weak security settings,” security researcher Vincent Li said. “Threat actors continue exploiting known vulnerabilities to gain initial access and deploy malware that can persist, spread, and cause distributed denial-of-service (DDoS) attacks.” This is not the first time the vulnerability has been exploited in the wild. Over the past year, the security issue has been leveraged to deploy a Mirai variant as well as a distinct, relatively new botnet called RondoDox.
The attack activity outlined by Fortinet involves the exploitation of CVE-2024-3721 to obtain and drop a downloader script, which then launches the botnet payload based on the Linux system’s architecture. Once the malware is executed, it displays a message stating “nexuscorp has taken control.” Nexcorium has a similar architecture to the Mirai variant, including XOR-encoded configuration table initialisation, watchdog module, and DDoS attack module. The malware also includes an exploit for CVE-2017-17215 to target Huawei HG532 devices in the network and incorporates a list of hard-coded usernames and passwords for use in brute-force attacks.
If the Telnet login is successful, it attempts to obtain a shell, set up persistence using crontab and systemd service, and connect to an external server to await commands for launching DDoS attacks over UDP, TCP, and SMTP. Once persistence is established on the device, the malware deletes the original downloaded binary to evade analysis. “The Nexcorium malware displays typical traits of modern IoT-focused botnets, combining vulnerability exploitation, support for multiple architectures, and various persistence methods to sustain long-term access to infected systems,” Fortinet said.
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