Incident Response Guide: Vidar Infostealer

Incident Triage Steps

Within the first 30 minutes, your priority is to determine the scope of the infection and assess potential data loss. Vidar typically operates as a secondary payload delivered via phishing, exploit kits, or bundled with pirated software. Begin by identifying the initial detection source-likely an alert from your EDR solution or a user report of unusual system behavior like high CPU usage or antivirus notifications.

Immediately query your SIEM platform for recent process creations matching known Vidar patterns. Look for processes with names like svchost.exe or explorer.exe running from unusual directories, particularly within %AppData%, %LocalAppData%, or %Temp%. Check for the creation of log files in %AppData%\Local\Temp\ or similar paths, as Vidar often stores stolen data in .log or .txt files before exfiltration.

To determine if data was exfiltrated, review outbound network connections from the past 24-48 hours. Vidar uses HTTP/HTTPS POST requests to communicate with its command-and-control (C2) servers. Search your proxy logs, firewall logs, or network monitoring tool for connections to domains with random alphanumeric strings or newly registered domains (NRDs). Look for POST requests containing encoded or encrypted data, especially to ports 443 or 8080. Check DNS logs for queries to suspicious domains, as Vidar may use DNS tunneling for data exfiltration. Identify any systems communicating with these indicators and immediately isolate them from the network.

Evidence Collection

Before initiating containment or eradication, preserve forensic evidence to support analysis and potential legal action. On each affected system, collect the following:

Memory Dumps: Use a trusted memory acquisition tool to capture a full RAM dump. This is critical as Vidar may store stolen credentials, browser sessions, and cryptocurrency wallet data in memory.

Process List and Disk Artifacts: Execute a command-line tool to list all running processes with their full command lines and hashes. Capture a snapshot of the filesystem, focusing on:

• %AppData%\Microsoft\Windows\Start Menu\Programs\Startup\ for persistence executables.
• %AppData%\Local\Temp\ and %Temp% for dropped binaries and log files (e.g., system.log, data.bin).
• User profile directories for stolen data archives (often .zip files).
• The Windows Registry. Export the following keys/hives:
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run
  • HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce
  • HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
  • HKCU\Software\Vidar (if present)

Network Evidence: Export all relevant logs from perimeter firewalls, web proxies, and internal network sensors for the past 7 days. Filter for the suspicious IPs and domains identified during triage. Preserve full packet captures (PCAPs) if available.

Vidar-Specific Artifacts: Search for and collect:

• Configuration files, often named config.json or cfg.dat, which may contain C2 addresses and stealer modules.
• Any files with recent timestamps containing structured data that appears to be browser cookies, saved passwords, or cryptocurrency keys.
• Scheduled Tasks or Windows Services created with random or misspelled names.

Containment Procedures

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

1. Network Segmentation: Immediately disconnect identified infected hosts from the network. If wholesale disconnection is disruptive, use network access control (NAC) or firewall rules to segment them into an isolated VLAN that blocks all outbound internet traffic except to a dedicated forensic/logging server. This prevents further C2 communication and data exfiltration.

2. Credential Reset Scope: Vidar steals credentials from browsers, email clients, FTP clients, and system vaults. Assume all credentials stored on or typed into an infected system are compromised. Initiate a password reset for:

   • Local administrator accounts on the infected machine.
   • Domain user accounts that were active on the machine.
   • All web services (corporate email, SaaS platforms, banking) where credentials were potentially autofilled or saved in the browser. Prioritize email and financial accounts.

3. C2 Blocking: Update your perimeter firewall, web proxy, and DNS security solutions to block all identified Vidar C2 domains and IP addresses. Implement sinkholing if possible. As Vidar operators often use domain generation algorithms (DGAs) or fast-flux networks, also consider blocking communication to newly seen domains or IPs in high-risk ASNs not required for business.

Eradication and Recovery

Eradication requires complete removal of Vidar components from all affected systems. Follow the detailed, step-by-step procedures outlined in the Vidar Removal Guide for per-system cleanup. This typically involves killing malicious processes, deleting persistent registry entries and scheduled tasks, and removing all dropped files and directories.

After executing the removal steps, restore systems from known-clean backups. Ensure backups predate the earliest evidence of infection. If clean backups are unavailable, rebuild systems from trusted installation media.

Verification is critical. Before returning a system to production:

1. Re-scan the system with updated antivirus and anti-malware scanners.
2. Validate that no anomalous processes, network connections, or persistence mechanisms remain.
3. Monitor the system closely in your EDR/SIEM for at least 48-72 hours for any recurrence of malicious activity.

Lessons Learned Checklist

After containment and eradication, conduct a formal review to improve defenses.

• Initial Infection Vector: How did Vidar enter the environment? Was it a malicious email attachment, a drive-by download, a compromised third-party software installer, or an infected removable drive? Analyze email gateway logs, web filter logs, and endpoint telemetry from the time of initial execution.
• Control Failures: Which security controls did not perform as expected?
  • Did email filtering fail to block the malicious attachment or link?
  • Was web filtering not configured to block malware-hosting or exploit kit domains?
  • Did endpoint protection not detect or prevent the execution of the Vidar payload?
  • Were application allowlisting or script-blocking policies not in place or bypassed?
• Detection Gaps: How long was the malware active before detection? Review logs to find the earliest execution timestamp and compare it to the first alert. Why wasn’t it detected sooner?
  • Were there no alerts for the creation of files in %AppData% or %Temp% from unusual parent processes?
  • Were network alerts for connections to suspicious domains not configured or tuned out?
  • Was behavioral detection for credential access from browser processes not enabled?
• Improvement Actions: Based on the answers above, define specific actions.
  • Technical: Implement or tighten controls for email attachment sandboxing, network egress filtering, and endpoint behavioral detection for process hollowing and credential dumping.
  • Process: Update incident response playbooks to include specific steps for infostealer incidents. Enhance user training to recognize phishing lures commonly used to distribute Vidar.
  • Monitoring: Create new correlation rules in your SIEM to detect the specific TTPs of Vidar, such as explorer.exe spawning cmd.exe to run PowerShell scripts, or rapid, sequential access to browser data files.

For proactive measures, refer to the Vidar Detection Guide. For more background on this threat, see the Vidar Overview.