Redline Stealer: A Technical Examination of Modern Malware Tactics

In this post, I’ll walk you through my analysis of a Redline Stealer malware sample. This journey spans both static and dynamic investigations, highlighting the various techniques this malware uses to evade detection, compromise system integrity, and potentially harvest sensitive data.

Basic Static Analysis

I started by examining the binary’s static properties. The sample is a 32-bit executable with the following characteristics:

• SHA-256:2ad1b5261442f87a5e7a1c53cd0335c61652b39da8f54587fe0adc45e0813661

• Entropy:7.956 – indicating a fairly packed or obfuscated binary.

• Notable Imports (as seen in PEStudio):

  • OpenClipboard

  • CloseClipboard

  • GetCurrentProcess

  These imports suggest clipboard operations, which later tied into potential data theft functionality.

• Interesting Strings:I noticed strings such as SetClipboardData, RemoveDirectory, and RegDeleteKey along with certificate URL references:

  ruby

  Copy

  Lhttp://cacerts.digicert.com/DigiCertTrustedG4RSA4096SHA256TimeStampingCA.crt0 5http://cacerts.digicert.com/DigiCertTrustedRootG4.crt0C

• Digital Signature:The specimen appears to be signed. However, further analysis later revealed issues with the signature.

  

  
  

Dynamic Analysis

Process Activity & File Operations

Using Procmon, I tracked the process tree during detonation. Here’s what I observed:

• Process Tree: The analysis started with cmd.exe launching immediately, which then spawned multiple processes. Notably, several new executables and a suspicious .pif file appeared.

  

• Temporary Directory Artifacts: In the appdata\local\temp directory, I found a collection of files with seemingly random names—ranging alphabetically from names starting with “a” up to “w”—along with a file named standard (later found to be a CMD script).

  

• Procdot Activity: A procdot capture (which I couldn’t capture entirely in one shot due to the volume of activity) showed extensive file creation in the temp folder.

  

• Other Notable File Activity: I discovered a file named “ConcertsOlympus” in the C:\Windows directory. Despite being 0 KB, its placement suggests it could be used to store or flag stolen data before it’s sent to a command-and-control (C2) server.

• Erroneous Folder Query: Procmon logged a failed attempt to query a folder named SuggestingCosmeticsContextRetrieveAndreasLooks, possibly related to an internal mechanism to check for a previous run of this malware on the machine.

  

• Sandbox/VM Folder Checks: The malware also probed for directories commonly found in virtualized or sandbox environments (e.g., chocolatey, node, python, CMDER), likely as a means of environment fingerprinting.

  

  
  

Command Execution

• CMD Invocation & File Renaming: One command that caught my eye was:

  bash

  Copy

  "C:\Windows\System32\cmd.exe" /k move Standard Standard.cmd & Standard.cmd & exit

  This command renames the file standard to standard.cmd (effectively making it executable) and then executes it immediately. This behavior likely explains the slew of “random” files in the temp folder—each potentially containing further malicious payloads or code.

  

• Task Enumeration: The malware leveraged tasklist.exe to enumerate running processes, probably as part of a security products check or to gather system context.

  

• Registry Operations: I observed RegSetInfoKey operations carried out by a child process (spawned by the malware), further hinting at system configuration changes for persistence or evasion.

  

• Security Software Enumeration: Using the Windows utility findstr, the malware executed several commands to search for the presence of known security products and modify them:

  1. First Invocation:

     findstr /I "wrsa.exe opssvc.exe"

     • wrsa.exe corresponds to Webroot SecureAnywhere.

     • opssvc.exe is related to Microsoft Operations Manager Service.

     

  2. Second Invocation:

     findstr /I "avastui.exe avgui.exe ekrn.exe bdservicehost.exe nswscsvc.exe sophoshealth.exe"

     This search is aimed at detecting popular antivirus and security applications such as Avast and AVG.

     

  3. Third Invocation:

     findstr /V "ForumsOpinionBalancedMissile" Config

     This command excludes the string ForumsOpinionBalancedMissile when scanning a file or directory named Config—its purpose remains unclear, but it could be part of an anti-analysis or obfuscation routine.

     

• AutoIt & PIF File: Another interesting finding was the creation of a process called Going.pif. PIF files, originally used for shortcut settings, are still treated as executables by Windows. Malware often leverages this quirk to bypass certain security filters. This particular file appears to be an AutoIt script—suggesting its use for payload execution, evasion, and persistence.

  

  Upon extracting strings from this file, I found several certificate-related references. Querying the registry key HKLM\SOFTWARE\Microsoft\SystemCertificates revealed a potentially suspicious certificate, aligning with the certificate strings observed earlier.

• 

• WSUS Hijacking & MITM Possibility: There are hints that the malware might be abusing WSUS (Windows Server Update Services) mechanisms, possibly to push fake updates. Although this behavior isn’t overtly aggressive in this sample, it could be a tactic to facilitate a man-in-the-middle (MITM) attack by intercepting SSL/TLS traffic and stealing credentials.

• Delay Tactics: The last child process observed was choice.exe running the command:

  choice /d y /t 5

  This introduces a deliberate delay (5 seconds) which is often used to thwart automated sandbox analyses.

  

Network Analysis via Wireshark

During the network traffic capture, several certificate requests were observed. However, one DNS resolution request particularly stood out:

hPcIqqFIRZncgBG.hPcIqqFIRZncgBG

This domain does not follow conventional naming patterns and strongly suggests that the malware employs a Domain Generation Algorithm (DGA). By generating domains on-the-fly, the malware can make it much harder for defenders to preemptively block its C2 communications.

Further Static Analysis

Digital Signature Verification

I ran sigcheck -a on the primary binary and found the following:

• Digital Signature Issue: The output reported:

  Digital Signature Failed (The digital signature of the object did not verify)

  Despite appearing to be signed by "Auslogics Labs Pty Ltd", the signature is invalid. This anomaly can indicate one or more of the following:

  • The certificate is either fake or has been revoked.

  • The binary was tampered with after signing.

  • A stolen code-signing certificate might have been used—a common tactic in sophisticated malware campaigns.

  

Advanced Static Insights via Ida Pro & x32dbg

• Clipboard Data Theft: Using Ida Pro, I noted that the malware imports functions such as SetClipboardData, OpenClipboard, and EmptyClipboard. This suggests that one of its objectives might be to steal or manipulate clipboard data—potentially targeting crypto wallet addresses or other sensitive data copied by the user.

  

• Registry Modifications: Analysis with x32dbg revealed changes in the registry, particularly in the Microsoft data collection options at:

  Software\Policies\Microsoft\Windows\DataCollection

  A registry query confirmed that this value was set to 0, effectively disabling Windows diagnostic data and telemetry—possibly to prevent Microsoft Defender from reporting or reacting to the malware’s presence.

• 

  

• AutoIt Payload Analysis: After unpacking and extracting the AutoIt file, I loaded it into Ida Pro. The disassembly showed API calls related to HttpSendRequestW and OpenFtpFileW, indicating that the payload could perform web and FTP requests—potentially to exfiltrate data or receive further instructions.

• 

  Obfuscated CMD File: Returning to the CMD file standard.cmd found in the temp folder, I attempted detonation. The execution resulted in an error. On inspecting its content, I noticed heavily obfuscated code—likely designed to resist detection and analysis.

  

  
  

Conclusion

This analysis of the Redline Stealer malware sample highlights a multi-faceted approach combining:

• Static obfuscation and invalid digital signatures that point towards tampering or the use of stolen certificates.

• Dynamic techniques such as renaming and executing obfuscated CMD scripts, extensive file creation in temporary directories, and leveraging PIF/AutoIt scripts for evasion and persistence.

• Security evasion methods, including probing for antivirus and monitoring processes, disabling Windows telemetry, and employing delays to frustrate sandbox environments.

• Network evasion through the use of DGAs, complicating efforts to track and block C2 domains.

  
  

Overall, this sample demonstrates sophisticated tactics aimed at both evading detection and enabling data exfiltration—possibly through clipboard monitoring and MITM attacks. As I continue to peel back its layers, further analysis of the individual payload components and network behaviors will be crucial to fully understand its impact and operational workflow.

Stay tuned for further updates as I delve deeper into the random files found in the temp folder and their respective roles in this intricate attack chain.

Happy hunting, and remember: in cybersecurity, the devil is always in the details.