New Forensic Method Reveals Hidden Traces of RDP Exploits by Hackers

Cybersecurity researchers have unveiled advanced techniques for tracking attackers who use Remote Desktop Protocol (RDP) to move laterally through compromised networks, turning the very technology hackers rely on into a digital fingerprint that reveals their every move.

The breakthrough centers on analyzing RDP’s bitmap caching mechanism, which stores 64×64 pixel tiles of remote screen images in cache files located in AppDataLocalMicrosoftTerminal Server ClientCache.

These .BMC and Cache**.bin files, originally designed to improve performance over slow connections, now serve as a treasure trove of forensic evidence showing exactly what attackers viewed during their sessions.

Event Log Forensics Reveal Hidden Patterns

Windows Event Logs provide the foundation for RDP investigation, with Event ID 4624 indicating successful logons and Event ID 4625 capturing failed attempts.

However, Network Level Authentication (NLA) creates a forensic complication: RDP connections initially appear as Logon Type 3 (Network) rather than the expected Type 10 (RemoteInteractive), potentially misleading investigators.

The TerminalServices-RemoteConnectionManager log records Event ID 1149 when users reach the login screen, while Event 21 in TerminalServices-LocalSessionManager confirms actual session establishment. These artifacts persist even when attackers attempt to cover their tracks.

Client-Side Artifacts Expose Attack Paths

On the source machine, investigators can examine the registry key HKCUSoftwareMicrosoftTerminal Server ClientServers to discover recently accessed RDP targets.

Jump Lists for mstsc.exe, stored in RoamingMicrosoftWindowsRecentAutomaticDestinations, maintain connection history that survives basic cleanup attempts.

The Default.rdp file in the user’s Documents folder contains plain-text configuration details for the last RDP session, including target IP addresses and usernames.

Specialized tools like BMC-Tools by France’s ANSSI and RdpCacheStitcher enable investigators to reconstruct attackers’ screen activity from cached bitmap fragments.

In one documented case, analysts recovered an entire sensitive document viewed by an Advanced Persistent Threat (APT) group by painstakingly reassembling thousands of image tiles.

The rdpclip.exe process, which handles clipboard synchronization between local and remote sessions, can retain copied passwords and sensitive data in memory.

Memory forensics tools like Volatility can extract this information, revealing credentials and commands that attackers copied during their sessions.

Even sophisticated attackers using cleanup scripts to delete registry keys, event logs, and cache files leave traces in unexpected places.

Device redirection events may log mapped printers or drives, potentially revealing the attacker’s origin network through printer names or domain paths.

This comprehensive forensic approach transforms RDP from an attacker’s stealth tool into a detailed audit trail.

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