All About Interwebz: Microsoft Exchange ProxyShell is being exploited to mine crypto once again

Hackers are using known ProxyShell vulnerabilities to install cryptocurrency miners on vulnerable Microsoft Exchange servers, researchers have claimed.

Cybersecurity experts from Morphisec observed unidentified attackers using ProxyShell (an umbrella term for multiple vulnerabilities that, when chained together, allow for remote code execution) to install XMRig on Microsoft Exchange servers.

XMRig is one of the most popular cryptocurrency mining malware variants, generating the Monero (XMR) cryptocurrency for attackers. Monero is a popular choice among cybercriminals because of its privacy features and the fact that it’s almost impossible to trace.

Hiding in plain sight

Morphisec says that the vulnerabilities used in this campaign are CVE-2021-34473 and CVE-2021-34523. Both of these were discovered, and patched, two years ago. Therefore, the best way to protect against these attacks is to apply the fix to vulnerable endpoints.

The attackers have also put in extra effort to make sure they remain hidden for as long as possible, the researchers said.

Once the miner is set up, it will create a firewall rule, applied to all Windows Firewall profiles, to block all outgoing traffic. That way, the researchers continued, the IT teams and other defenders won’t be notified of the breach in the system.

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Furthermore, the malware will wait at least 30 seconds between starting the mining process and creating the firewall rule, to evade triggering alarms from security tools that monitor process runtime behavior.

Cryptocurrency miners won’t destroy a computer, but as they take up almost all of the computing power, will render the device practically useless. What’s more, they could rake up enormous electricity bills for the computers’ owners.

Morphisec also said that vulnerable Microsoft Exchange server owners shouldn’t take the attack lightly, as after making their way into the network, there’s nothing stopping the attackers from deploying any other form of malware.