Hijacked by RapperBot: Devices Exploited for Instant DDoS Attacks

Cybersecurity: RapperBot Malware Analysis

A new variant of the RapperBot malware is exploiting internet-connected devices, particularly outdated network video recorders (NVRs), to form a distributed denial-of-service (DDoS) network. This extensive network can be established rapidly.

Technical Details

Security researchers have identified an advanced exploit chain that uses zero-day vulnerabilities, outdated firmware, and alternative DNS infrastructures. This allows the orchestration of attacks with traffic volumes exceeding terabit scales.

The RapperBot scanning infrastructure quickly identifies vulnerable DVR and NVR models by scanning the internet for exposed web servers. Once targeted, the malware employs a two-stage exploit process. This includes a path-traversal flaw in the device’s HTTP service to obtain administrator credentials, followed by a fake firmware update via TCP port 34567.

The malicious update mounts a remote NFS share and executes the payload directly in memory, ensuring no persistent filesystem footprint. This method circumvents common detection measures by utilizing NFS, a tool supported by many embedded devices lacking capabilities like wget or curl.

RapperBot now uses a custom-encrypted DNS TXT record mechanism instead of hard-coding command-and-control (C2) IP addresses. This innovation involves generating one of 32 fully qualified domain names under uncommon top-level domains such as .live and .info. It then queries OpenNIC resolvers to retrieve an encrypted TXT record with a list of C2 servers.

Blindingly Fast DDoS Weaponization

After establishing a C2 connection, typically on port 4444 but including a broad range such as 1935, 3478, 5000, and 37777, the botnet controller commands network scanning and UDP-flood attacks on port 80. Analysis shows additional TCP scans on port 23.

Infected NVRs can initiate high-volume packet streams almost immediately. Even aged 10 Mbit hubs can passively sniff traffic, facilitating stealthy attack pattern analysis.

RapperBot has been linked to significant multi-terabit per second traffic surges against major platforms. It maintains a constantly refreshed botnet by reinfecting rebooted devices swiftly.

The malware’s infrastructure shows periodic IP address rotation for scanners, repositories, and C2 servers. It supports FTP and HTTP access on port 21, enhancing compatibility with minimal environments. Domain pivots indicate a geographically diverse infrastructure.

On August 19, 2025, a U.S. resident was charged in connection with the operation of the RapperBot network, as part of Operation PowerOFF.

Defending Against the Next Wave

1. Replace or isolate legacy NVRs and DVRs to minimize risk.
2. Disable UPnP and review router port mappings to prevent exposure.
3. Implement strong, unique passwords and change default credentials on all devices.
4. Monitor DNS traffic for unusual TXT queries to unauthorized resolvers.
5. Use IDS/IPS solutions to detect abnormal UDP floods and scanning activities.

While the widespread nature of these threats means they will persist, understanding RapperBot’s tactics can help network defenders anticipate and mitigate sudden DDoS attacks.