Pierluigi Paganini May 10, 2020

Crooks exploit CVE-2019-18935 deserialization vulnerability to achieve remote code execution in Blue Mockingbird Monero-Mining campaign.

Researchers at security firm Red Canary uncovered a Monero cryptocurrency-mining campaign, tracked as Blue Mockingbird, that exploits the CVE-2019-18935 vulnerability in web applications built on the ASP.NET framework.

The deserialization vulnerability CVE-2019-18935 could be exploited by attackers to achieve remote code execution, it affects the Progress Telerik UI for ASP.NET AJAX and was also mentioned in a joint report released by the U.S. NSA and the Australian Signals Directorate (ASD) warning of attackers increasingly exploiting vulnerable web servers to deploy web shells.

This issue could be exploited only when the encryption keys are obtained via a separate attack, meaning that the attackers have to chain more exploits in their campaigns.

“Blue Mockingbird is the name we’ve given to a cluster of similar activity we’ve observed involving Monero cryptocurrency-mining payloads in dynamic-link library (DLL) form on Windows systems.” reads the report published by Red Canary experts. “They achieve initial access by exploiting public-facing web applications, specifically those that use Telerik UI for ASP.NET, followed by execution and persistence using multiple techniques “

Hackers targeted vulnerable versions of Telerik UI for ASP.NET to deploy the XMRig Monero-mining payload as a DLL on Windows systems. Experts also noticed that once compromised the system, attackers attempt lateral movements.

According to the experts, the Blue Mockingbird campaign is dated back at leak December 2019 and is still ongoing.

The researchers observed three distinct uses:

• Execution with rundll32.exe explicitly calling the DLL export fackaaxv;
• Execution using regsvr32.exe using the /s command-line option;
• Execution with the payload configured as a Windows Service DLL.

“Each payload comes compiled with a standard list of commonly used Monero-mining domains alongside a Monero wallet address,” continues the analysis. “So far, we’ve identified two wallet addresses used by Blue Mockingbird that are in active circulation. Due to the private nature of Monero, we cannot see the balance of these wallets to estimate their success.”

In order to achieve persistence, attackers first elevate their privileges with different techniques (using a JuicyPotato exploit to escalate privileges from an IIS Application Pool Identity virtual account to the NT Authority\SYSTEM account, stealing access credentials using the Mimikatz tool).

Then attackers use multiple persistence techniques, including the use of a COR_PROFILER COM hijack to execute a malicious DLL and restore items removed by defenders.

Blue Mockingbird threat actors move laterally by elevating privileges and using Remote Desktop Protocol (RDP) to access privileged systems and Windows Explorer to deploy the malicious payloads to remote systems.

Researchers speculate that attackers’ toolkit are still under active development.

“For mitigations, focus on patching web servers, web applications, and dependencies of the applications. Most of the techniques used by Blue Mockingbird will bypass whitelisting technologies, so the best route will be to inhibit initial access. Consider establishing a baseline of Windows Scheduled Tasks in your environment to know what is normal across your enterprise.” concludes the report.

Researchers also included Indicators of Compromise (IoCs) in the analysis they have published.

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Pierluigi Paganini

(SecurityAffairs – Blue Mockingbird, hacking)

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