Full Report
Discover how a seemingly simple brute force attack led to the uncovering of a suspected ransomware-as-a-service operation. This ecosystem appears to be leveraged by initial access brokers, driving an illicit and complex network of cybercrime.
Analysis Summary
# Tool/Technique: RDP Brute Force & Domain Enumeration (IAB Tradecraft)
## Overview
This report details an intrusion identified by the Huntress SOC involving a successful brute force attack against a publicly exposed Remote Desktop Protocol (RDP) server. The activity is characteristic of **Initial Access Brokers (IABs)**, who specialize in gaining entry to corporate networks and performing preliminary reconnaissance before selling that access to Ransomware-as-a-Service (RaaS) affiliates.
## Technical Details
- **Type**: Technique (Brute Force / Enumeration) and Tooling (IAB Infrastructure)
- **Platform**: Windows (Active Directory environments)
- **Capabilities**: Credential harvesting, automated brute-forcing via distributed infrastructure, and domain reconnaissance.
- **First Seen**: Reported April 10, 2025 (Event observed recently prior to publication).
## MITRE ATT&CK Mapping
- **TA0001 - Initial Access**
- T1133 - External Remote Services
- **TA0006 - Credential Access**
- T1110.001 - Brute Force: Password Guessing
- **TA0007 - Discovery**
- T1087.002 - Account Discovery: Domain Account
- T1069.002 - Permission Groups Discovery: Domain Groups
- T1482 - Domain Trust Discovery
## Functionality
### Core Capabilities
- **Distributed Brute Forcing**: The threat actor utilized multiple rotating IP addresses to conduct password-guessing attacks, likely to bypass simple rate-limiting or IP-based blocking.
- **External Access Exploitation**: Targeting default RDP ports (TCP 3389) exposed to the internet.
- **Automated Enumeration**: Rapid execution of commands to map the victim's domain structure immediately following a successful login.
### Advanced Features
- **Infrastructure Abstraction**: Use of a "larger ransomware ecosystem" infrastructure, which allows the actor to pivot through various servers, masking the true origin of the attack and complicating attribution.
## Indicators of Compromise
- **File Names**: The article highlights the use of standard Windows utilities for discovery (e.g., `net.exe`, `nltest.exe`).
- **Network Indicators**:
- Multiple disparate IP addresses (defanged examples: `193.233.202[.]x`, `45.128.232[.]x` — *Note: specific IPs are often unique to the incident; the pattern shows high-volume rotation*).
- RDP traffic originating from non-standard geographic locations relative to the business.
- **Behavioral Indicators**:
- `4625` Windows Security Events (Failed Logins) followed by a `4624` (Successful Login) for the same user from an external IP.
- Execution of `net group "Domain Admins" /domain` or similar reconnaissance commands shortly after RDP authentication.
## Associated Threat Actors
- **Initial Access Brokers (IABs)**: Unnamed specific group, but linked to broader **Ransomware-as-a-Service (RaaS)** operations.
## Detection Methods
- **Signature-based detection**: Monitoring for "Net" commands used in rapid succession (e.g., `net group`, `net user`).
- **Behavioral detection**:
- Monitoring for high volumes of failed RDP login attempts (Event ID 4625) followed by a successful login (Event ID 4624) from the same source.
- Alerting on successful logins from IPs with poor reputations or locations that do not match known employee patterns.
## Mitigation Strategies
- **Prevention measures**:
- Implement Multi-Factor Authentication (MFA) for all external-facing services, especially RDP.
- Place RDP servers behind a VPN or a Gateway rather than exposing them directly to the internet.
- **Hardening recommendations**:
- Enforce strong, complex password policies to increase the time required for a successful brute force.
- Implement Account Lockout Policies to temporarily disable accounts after a specific number of failed attempts.
## Related Tools/Techniques
- **NLTEST**: Used for querying domain controllers and testing trust relationships.
- **BloodHound/SharpHound**: Advanced tools often used by IABs for deeper domain mapping (though not explicitly mentioned in this specific snippet).
- **Mimikatz**: Often used post-access for further credential theft.