Full Report
A new variant of the Gafgyt botnet called C0XMO is targeting DD-WRT router firmware and can move to other device types with various CPU architectures. [...]
Analysis Summary
# Tool/Technique: C0XMO (Gafgyt Variant)
## Overview
C0XMO is an advanced variant of the Gafgyt (also known as BASHLITE) IoT botnet. Its primary purpose is to recruit compromised devices into a botnet to launch large-scale Distributed Denial-of-Service (DDoS) attacks. It distinguishes itself from earlier iterations through a modular design, broad architectural support, and aggressive "self-defense" mechanisms that terminate competing malware.
## Technical Details
- **Type**: Malware family (Botnet / DDoS)
- **Platform**: Multi-platform/CPU architectures (ARM, MIPS, PowerPC, SuperH, x86, x86_64); specifically targets DD-WRT firmware, DVRs, and Android-based devices.
- **Capabilities**: DDoS (19 methods), vulnerability exploitation (CVE-2021-27137), SSH/Telnet brute-forcing, lateral movement, process termination (competitor removal), and persistence.
- **First Seen**: June 2026 (per article reporting)
## MITRE ATT&CK Mapping
- **[TA0001 - Initial Access]**
- [T1190 - Exploit Public-Facing Application]
- [T1110.001 - Brute Force: Password Cracking]
- **[TA0003 - Persistence]**
- [T1053.003 - Scheduled Task/Job: Cron]
- [T1546.004 - Event Triggered Execution: Unix Shell Configuration Scripts]
- **[TA0008 - Lateral Movement]**
- [T1021.004 - Remote Services: SSH]
- **[TA0005 - Defense Evasion]**
- [T1562.001 - Impair Defenses: Disable or Modify Tools] (Terminating rival botnets/security tools)
- [T1070.004 - Indicator Removal: File Deletion]
- **[TA0011 - Command and Control]**
- [T1573.001 - Encrypted Channel: Non-Standard Cryptography] (Custom handshake/shared secrets)
- **[TA0040 - Impact]**
- [T1498.001 - Network Denial of Service: Direct Network Flood]
## Functionality
### Core Capabilities
- **Multi-Method DDoS**: Supports 19 different attack vectors, including UDP/TCP/SYN/ICMP floods, "Ping of Death," and amplification attacks (NTP/Memcached).
- **Vulnerability Exploitation**: Leverages CVE-2021-27137 (a buffer overflow in DD-WRT) to achieve unauthenticated remote code execution (RCE).
- **Scanner Module**: Uses a Python-based scanner to identify internet-facing targets via common ports (22, 23, 80, 443, 7547, 8080, etc.).
- **Brute Forcing**: Attempts to gain access via weak Telnet and SSH credentials.
### Advanced Features
- **Modular Design**: Operators can update exploitation modules and target architectures independently of the main binary.
- **Competitor Elimination**: Scans for and terminates processes related to rival botnets, red-team tools, and network services to monopolize device resources.
- **Infrastructure Awareness**: Detects the CPU architecture of a target device to deploy the specific compatible binary.
- **C2 Stealth**: Uses a custom multi-stage handshake involving "magic strings" and shared secrets to communicate with the C2 server.
## Indicators of Compromise
- **File Hashes**: (Specific hashes not provided in text; typically vary by architecture)
- **File Names**:
- `/tmp/.sys`
- `/var/tmp/.sys`
- `/dev/shm/.sys`
- **Network Indicators**:
- Port 22 (SSH), 23 (Telnet), 7547, 8080, 8443, 8888 (Inbound/Outbound scanning)
- C2 communication: Hardcoded addresses (e.g., `example[.]com` - *Defanged*)
- **Behavioral Indicators**:
- Creation of unauthorized cron jobs.
- Modification of `.bashrc` or profile scripts.
- Unexpected termination of system services or other malware processes.
## Associated Threat Actors
- Not specifically named in the report, though associated with the evolution of **Gafgyt/BASHLITE** operators.
## Detection Methods
- **Signature-based detection**: Monitoring for the specific magic strings used during the C2 handshake and unique binary strings.
- **Behavioral detection**:
- Identifying numerous outbound connection attempts on ports 22, 23, and 8080.
- Monitoring for unauthorized modifications to `/etc/crontab` or hidden files in `/tmp`.
- **YARA rules**: Rules should focus on the 19 DDoS method strings and the unique Python scanner script functions.
## Mitigation Strategies
- **Patch Management**: Immediately update DD-WRT firmware to remediate CVE-2021-27137.
- **Credential Hygiene**: Replace default or weak factory passwords with strong, unique credentials for SSH and web interfaces.
- **Access Control**: Disable Telnet and remote SSH access from the WAN; use VPNs for remote management.
- **Network Segmentation**: Isolate IoT devices and routers from critical data segments to prevent lateral movement.
## Related Tools/Techniques
- **Gafgyt (BASHLITE)**: The original malware family.
- **Mirai**: Often competes for the same IoT devices and uses similar scanning techniques.
- **NTP/Memcached Amplification**: Techniques utilized by C0XMO for high-volume DDoS.