CVE-2019-2725 Oracle WebLogic flaw exploited in cryptojacking campaign

Pierluigi Paganini June 11, 2019

The CVE-2019-2725 vulnerability in Oracle WebLogic recently, addressed by the company, is being exploited in cryptojacking attacks, Trend Micro reports.

Experts at Trend Micro reported that the recently patched CVE-2019-2725 vulnerability in Oracle WebLogic is being exploited in cryptojacking attacks.

The flaw is a deserialization remote command execution zero-day vulnerability that affects the Oracle WebLogic wls9_async and wlswsat components.

The issue affects all Weblogic versions, including the latest one, that have the wls9_async_response.war and wls-wsat.war components enabled.

Oracle WebLogic Server is a Java EE application server currently developed by Oracle Corporation, it is used by numerous applications and web enterprise portals based on Java technology.

An attacker could exploit the vulnerability to remotely execute commands without authorization by sending a specially crafted HTTP request.

The CVE-2019-2725 flaw was patched in late April, unfortunately, a few days later threat actors started exploiting the Oracle WebLogic Server vulnerability to deliver the Sodinokibi ransomware.

After the publication of the security advisory, experts at the SANS Institute reported that the flaw was already being actively exploited in cryptojacking campaigns. Experts at Trend Micro now confirm the SANS report and add that attackers are using an interesting obfuscation technique.

The malware used in this campaign hides its malicious codes in certificate files to evade detection.

CVE-2019-2725 cryptojacking

Once the malware is executed it exploits the CVE-2019-2725 flaw to execute a command and perform a series of routines. 

“The purpose of the command is to perform a series of routines. First, PowerShell (PS) is used to download a certificate file from the command-and-control (C&C) server and save it under %APPDATA% using the file name cert.cer (detected by Trend Micro as Coinminer.Win32.MALXMR.TIAOODCJ.component).” reads the analysis published by Trend Micro.

“It then employs the component CertUtil, which is used to manage certificates in Windows, to decode the file.”

The attack chains starts with a PowerShell that downloads a certificate file from the C2 server. The malicious code uses the CertUtil tool to decode the file, then execute it using PowerShell. The downloaded file is then deleted using cmd.

The certificate file appears as a Privacy-Enhanced Mail (PEM) format certificate, it is in the form of a PowerShell command instead of the X.509 TLS file format.

“One interesting characteristic of the downloaded certificate file is that it requires that it be decoded twice before the PS command is revealed, which is unusual since the command from the exploit only uses CertUtil once.” continues the experts. “There is also the possibility that the certificate file we downloaded is different from the file that was actually intended to be downloaded by the remote command, perhaps because it is continuously being updated by the threat actors.”

The command in the certificate file is used by crooks to download and execute another PowerShell script in memory. The script downloads and executes multiple files, including Sysupdate.exe (Monero miner), Config.json (configuration file for the miner), Networkservice.exe (likely used for propagation and exploitation of WebLogic), Update.ps1 (the PowerShell script in memory), Sysguard .exe (watchdog for the miner process), and Clean.bat (deletes other components). 

Experts noticed that the update.ps1 file that contains the decoded certificate file is replaced with the new update.ps1 and a scheduled task is created to execute the new PowerShell script every 30 minutes.

The idea of hiding malware into certificate is not a novelty, experts at Sophos explored this technique in a proof of concept late last year.

“However, oddly enough, upon execution of the PS command from the decoded certificate file, other malicious files are downloaded without being hidden via the certificate file format mentioned earlier.” concludes Trend Micro. “This might indicate that the obfuscation method is currently being tested for its effectiveness, with its expansion to other malware variants pegged at a later date,”

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Pierluigi Paganini

(SecurityAffairs – CVE-2019-2725, Oracle WebLogic)

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