Thursday, December 7, 2023

Hackers Exploit ProxyShell Flaws to Deploy ProxyShellMiner on Exchange Server

ProxyShellMiner is being distributed to Windows endpoints by a very elusive malware operation, according to Morphisec.

To generate income for the attackers, “ProxyShellMiner” deploys cryptocurrency miners throughout a Windows domain using the Microsoft Exchange ProxyShell vulnerabilities.

ProxyShellMiner exploits a company’s Windows Exchange servers using the ProxyShell vulnerabilities CVE-2021-34473 and CVE-2021-34523 to get initial access and distribute crypto miners.

“After successfully breaching an Exchange server and obtaining control, the attackers use the domain controller’s NETLOGON folder to ensure the miner executes throughout the domain, similar to how software is delivered through GPO”, Morphisec reports.

Researchers noticed that the attackers were utilizing four C2 servers. The legitimate, infected mail servers are all where the malware-dependent files are stored.

“Mining cryptocurrency on an organization’s network can lead to system performance degradation, increased power consumption, equipment overheating, and can stop services”, according to Morphisec.

Technical Analysis of the ProxyShellMiner Malware

The malware needs a command line parameter that acts as a password for the XMRig miner component in order to activate.

“This parameter is later used as a key for the XMRig miner configuration, and as an anti-runtime analysis tactic”, Morphisec

The parameter serves as anti-analysis technique, and as a password for the XMrig miner
The parameter serves as an anti-analysis technique and as a password for the XMrig miner

The XOR decryption algorithm, an XOR key, and an embedded dictionary are all used by ProxyShellMiner. The subsequent embedded code modules are then executed using the C# compiler CSC.exe with “InMemory” compile parameters.

The malware then downloads a file with the name “DC DLL” and uses .NET reflection to get the task scheduler, XML, and XMRig key arguments. The decryption of additional files is done using the DLL file.

By setting up a scheduled activity to start when the user logs in, a second downloader achieves persistence on the compromised system. The report says four other files and the second loader are downloaded from a remote resource.

The deobfuscated scheduled task 
The deobfuscated scheduled task

Using a technique called “process hollowing,” that file determines which of the installed browsers on the hacked system would be used to inject the miner into its memory space. The mining process then starts after selecting a random mining pool from a hardcoded list.

Picking a mining pool
Picking a mining pool

Setting a firewall rule that blocks all outgoing traffic and is applicable to all Windows Firewall profiles is the last stage in the attack chain. This is done to reduce the likelihood that defenders may find infection signs or get notifications about a possible compromise from the compromised system.

“The malware waits at least 30 seconds while the target machine blocks any outbound connection. It does this to tamper with the process runtime behavior analysis of common security solutions”, researchers.

Adding a firewall rule to block all outgoing traffic
Adding a firewall rule to block all outgoing traffic

Final Thoughts

ProxyShellMiner doesn’t just disrupt business networks, drive up power bills, overheat equipment, and stop services from operating. It gives threat actors access to further evil purposes.

“Once attackers have a foothold in a network, they have deployed web shells, backdoors, and used tunneling utilities to further compromise victim organizations”, Morphisec

Hence, Morphisec encourages all administrators to install all available security updates and employ thorough and all-encompassing threat detection and defense measures to reduce the danger of ProxyShellMiner attacks.

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