Threat actors have leveraged the Nitrogen ransomware campaign to target organizations through deceptive malvertising strategies.
Recent investigations have uncovered a disturbingly effective method involving fake software downloads, such as a counterfeit “WinSCP” installer, propagated through malicious ads on platforms like Bing.
One documented case revealed a user searching for “WinSCP download” via Microsoft Edge being redirected from ftp-winscp[.]org to a compromised WordPress site.
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This site hosted a malicious ZIP file, WinSCP-6.3.6-Setup.zip (SHA-256: fa3eca4d53a1b7c4cfcd14f642ed5f8a8a864f56a8a47acbf5cf11a6c5d2afa2), which bundled legitimate DLLs with a malicious python312.dll.
Upon execution, this triggered DLL sideloading, installing WinSCP in the foreground while covertly loading the NitrogenLoader DLL, establishing an initial foothold for a broader attack chain that ultimately deployed BlackCat ransomware.
Cobalt Strike Beacons and Log Clearing Thwart Detection Efforts
Further forensic analysis of compromised systems revealed the extensive use of Cobalt Strike, a notorious post-exploitation framework, to facilitate lateral movement and maintain persistence within targeted networks.
Investigators identified suspicious executables like Intel64.exe and tcpp.exe on “patient zero” systems, with tools like THOR flagging potential Cobalt Strike configurations through byte patterns such as the recurring XOR key 0x2e.
Decryption using CyberChef and parsing with Sentinel One’s CobaltStrikeParser exposed internal IP addresses and beacons pivoting through patient zero, often using sacrificial processes like gpupdate.exe for payload injection.
A watermark (678358251) linked to multiple threat actors, including Black Basta, underscored the reused infrastructure across campaigns.
Adding to the complexity, threat actors actively cleared critical Windows event logs-Security, System, and PowerShell-on compromised hosts to obscure their tracks.
However, User Access Logging (UAL) entries in supertimelines and Windows Error Reporting (WER) crash dumps, analyzed via WinDBG, provided crucial evidence of lateral movement and Cobalt Strike activity within memory dumps of processes like svchost.exe.
Advanced Forensic Techniques Uncover Hidden Threats
The depth of these attacks necessitated advanced forensic workflows, blending automated tools like Velociraptor for triage with manual analysis of crash dumps and memory structures like the Process Environment Block (PEB).
Strings extracted from crash dumps using bstrings.exe revealed Cobalt Strike HTTP responses and team server URLs, while YARA rules helped pinpoint malicious binaries in memory.
Despite challenges like incomplete memory dumps due to paging, the combined indicators-ranging from suspicious executables to encrypted configurations-confirmed the persistent threat posed by Nitrogen.
As tools like THOR evolve with features to automate Cobalt Strike detection in upcoming versions (e.g., THOR v11), the cybersecurity community braces for more sophisticated attacks.
Organizations are urged to bolster defenses against malvertising, monitor for anomalous DLL loading, and preserve forensic artifacts to mitigate the devastating impact of ransomware campaigns exploiting trusted software downloads and powerful frameworks like Cobalt Strike.
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