This rule detects the presence of the VxSK YARA signature, which typically identifies specific malicious executables or in-memory code patterns associated with known threat actors. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify dormant or low-noise malware instances that may have evaded traditional network-based detections, ensuring early containment of potential compromises.
rule VxSK
{
meta:
author="malware-lu"
strings:
$a0 = { CD 20 B8 03 00 CD 10 51 E8 00 00 5E 83 EE 09 }
condition:
$a0 at pe.entry_point
}This YARA rule can be deployed in the following contexts:
This rule contains 1 string patterns in its detection logic.
Scenario: A legitimate Java application (e.g., a custom internal ERP system or a legacy banking module) is deployed using a standard jar file that has been repackaged or obfuscated by a build tool like Maven or Gradle. The YARA rule VxSK likely targets specific byte patterns or string signatures common in Java archives or specific class file structures, causing the scanner to flag the .jar or .class files as malicious.
.jar, .war, or .ear extensions from the scan scope, or specifically exclude paths containing target/, build/, or dist/ directories where compiled Java artifacts are stored.Scenario: An enterprise backup solution (such as Veeam, Commvault, or Acronis) creates temporary snapshot files or deduplicated data blocks on the file server. These blocks may contain fragmented or compressed data that coincidentally matches the byte pattern or string signature defined in the VxSK rule, especially if the rule looks for specific header bytes or entropy-based characteristics.
\Backup\, \Veeam\, \Commvault\) or exclude files with extensions like .vbk, .vib, .dat, or .block that are known to be part of the backup infrastructure.Scenario: A developer or DevOps engineer uses a container image registry (like Docker or Harbor) and pulls an image that contains a specific library or binary (e.g., a Go-compiled binary or a C++ shared object) that has a unique section header or string sequence matching the VxSK signature. This often happens when a custom-built microservice is pushed to the registry and then deployed to a Kubernetes node.