Incident Response Guide: RedLine Stealer

Incident Triage Steps

Within the first 30 minutes, your priority is to determine the scope of the incident and confirm if data exfiltration occurred. RedLine Stealer typically spreads via phishing emails with malicious attachments, cracked software, or fake installers. Begin by interviewing the initial reporter to identify the suspected entry point, such as a downloaded file or email attachment.

Immediately query your EDR solution or endpoint logs for known RedLine indicators. Search for processes with names like “chrome.exe” or “firefox.exe” running from unusual directories (e.g., %AppData%, %LocalAppData%, %Temp%). Check for the creation of scheduled tasks or Windows services with random, alphanumeric names. Examine network logs for outbound connections to known RedLine C2 infrastructure, which often uses HTTP/S on non-standard ports (e.g., 8080, 8443) and communicates with domains that mimic legitimate cloud services or use newly registered domains (NRDs). A key triage step is to check for large, unexpected outbound data transfers from user workstations, as RedLine exfiltrates stolen data in compressed archives.

To identify affected systems, run a cross-host search for the execution of suspicious PowerShell scripts or the use of curl or bitsadmin for downloads. Review authentication logs for anomalous login attempts, as RedLine harvests credentials from browsers, FTP clients, and cryptocurrency wallets. Check if any system has recently had antivirus or logging services unexpectedly disabled. Scope should initially focus on the initially reported machine and any systems with similar recent user activity or network connections.

Evidence Collection

Before any remediation, preserve the following evidence for forensic analysis. On each potentially infected system:

1. Memory Capture: Use a trusted memory acquisition tool to capture a full RAM dump. RedLine often injects its payload into legitimate processes, and key artifacts like decrypted strings or C2 addresses may only reside in memory.
2. Volatile Data: Collect a running process list (noting PID, PPID, command line, and hash), network connections (especially ESTABLISHED outbound), and a list of recently run commands via console history or PowerShell logs.
3. Disk Forensics: Image the system drive if a full incident is declared. For targeted collection, focus on:
   • Files: Collect any suspicious executables, DLLs, or scripts from %Temp%, %AppData%, %LocalAppData%, and the user’s Downloads folder. RedLine droppers often have names like setup.exe, installer.msi, or crack.exe.
   • Registry: Export registry hives, particularly focusing on autostart persistence locations RedLine uses:
     • HKCU\Software\Microsoft\Windows\CurrentVersion\Run
     • HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce
     • Scheduled Tasks (check %Windows%\System32\Tasks)
   • Logs: Collect Windows Event Logs (especially Security, System, and PowerShell Operational), firewall logs, and any application logs from breached software (e.g., browser histories).
4. Network Evidence: Preserve full packet captures (PCAPs) from border and internal network sensors, focusing on traffic to/from the suspected infected hosts. Export proxy logs, DNS query logs, and firewall connection logs for the incident timeframe. RedLine C2 traffic may contain specific URI patterns or user-agent strings.
5. RedLine-Specific Artifacts: Search for and collect the stolen data cache, which RedLine often places in a temporary folder before exfiltration, with names like data.zip or logs.rar. Also, collect any configuration files, which may be found in %AppData% or %LocalAppData% with .cfg or .bin extensions.

Containment Procedures

Containment aims to halt the malware’s spread and data theft without destroying evidence.

1. Network Segmentation: Immediately isolate the confirmed infected hosts from the network. Use network access control or VLAN changes to place them in a quarantine segment with no internet or internal network access. If isolation is not immediately possible, block all outbound traffic from the host at the firewall except to designated forensic and management networks.
2. Credential Reset: RedLine steals a wide array of credentials. Scope credential resets by first analyzing the malware’s configuration from collected artifacts to see which applications were targeted. At a minimum, force password resets for:
   • All domain and local accounts active on the infected machine.
   • Any credentials found in browser password managers, FTP clients (like FileZilla), and email clients on that host.
   • Any associated corporate cloud accounts (e.g., email, CRM, VPN) used from that system. Consider resetting session tokens as well.
3. C2 Blocking: Update firewall, proxy, and DNS sinkhole rules to block communication with identified RedLine C2 servers. Use indicators from your network logs and threat intelligence feeds. Block the IP addresses and domains. RedLine may use dynamic DNS or fast-flux domains, so implement rules to block traffic to the associated IP ranges and continue monitoring for new C2 domains.
4. Temporary Mitigations: On potentially exposed but not yet confirmed systems, consider temporarily disabling non-essential scheduled tasks and increasing monitoring on autostart registry locations.

Eradication and Recovery

Eradication requires complete removal of RedLine Stealer and its components from all affected systems.

1. Complete Removal: Follow the detailed, step-by-step procedures outlined in the dedicated Removal Guide. This guide provides per-system instructions for killing malicious processes, deleting persistent artifacts, and removing scheduled tasks or services created by the malware.
2. Restoration: For critically infected systems or where you cannot guarantee eradication, rebuild the operating system and applications from known-clean, offline backups. Ensure backups are from a date prior to the earliest evidence of infection. Do not restore user data files (documents, downloads) without scanning them with multiple anti-malware engines, as RedLine may have been delivered via a malicious document.
3. Verification: After eradication or restoration, verify a clean state. Perform a full system scan with an updated anti-malware solution. Re-examine the system for the persistence mechanisms and file artifacts listed in the removal guide. Monitor the host’s network traffic for several days to ensure no further beaconing to C2 infrastructure occurs. Use a SIEM platform to correlate logs from the cleaned system with network alerts for any residual malicious activity.

Lessons Learned Checklist

After containment and eradication, conduct a post-incident review to improve defenses.

• Initial Access: How did RedLine Stealer gain entry? Was it a phishing email, a drive-by download, or a malicious download from a third-party site? Which user or system was the patient zero?
• Control Failures: What security controls failed or were absent?
  • Was email filtering not configured to block the malicious attachment type?
  • Did application allowlisting fail to prevent execution from %Temp%?
  • Were network defenses not alerting on connections to known malicious IPs/domains?
  • Was endpoint detection not configured to alert on process injection or credential access from unusual locations?
• Detection Gaps: How was the malware discovered? Was it via an alert, user report, or external notification? How long was it present before detection? Review logs to see if missed alerts were present.
• Improvement Plan:
  • Technical: Can you implement stricter execution policies (e.g., blocking executable launches from user writable directories)? Can you improve network monitoring for data exfiltration patterns? Should you deploy enhanced credential theft protection?
  • Process: Does your incident response plan need updating based on this experience? Were evidence collection procedures adequate?
  • Training: Does user awareness training need strengthening regarding phishing and downloading software from unofficial sources?

For detailed steps on finding and removing RedLine Stealer from individual computers, refer to the Removal Guide. To understand its behaviors and implement detection, see the Detection Guide. For general information about this threat, visit the RedLine Stealer Overview.