This rule identifies the presence of the RCryptor ransomware variant, which typically encrypts files and appends a specific extension to lock user access to critical data. Proactively hunting for this signature allows the SOC team to detect early-stage infections or dormant payloads before the encryption process begins, minimizing potential data loss and operational disruption.
rule RCryptorv1Vaska
{
meta:
author="malware-lu"
strings:
$a0 = { 90 58 90 50 90 8B 00 90 3C 50 90 58 0F 85 67 D6 EF 11 50 68 }
$a1 = { 90 58 90 50 90 8B 00 90 3C 50 90 58 0F 85 67 D6 EF 11 50 68 [4] B8 [4] 3D [4] 74 06 80 30 ?? 40 EB F3 }
condition:
$a0 at pe.entry_point or $a1 at pe.entry_point
}This YARA rule can be deployed in the following contexts:
This rule contains 2 string patterns in its detection logic.
Scenario: A developer or DevOps engineer runs the vaska encryption tool locally on a build agent or CI/CD pipeline worker to encrypt sensitive configuration files or artifacts before deployment.
msbuild.exe, dotnet.exe, npm.exe, docker.exe) or where the process path resides within standard build directories (e.g., C:\builds\, C:\jenkins\workspace\).Scenario: An IT administrator uses vaska as part of a scheduled PowerShell script to encrypt backup logs or audit trails before archiving them to a NAS or cloud storage.
backup, archive, log) or where the parent process is powershell.exe or pwsh.exe and the working directory matches known backup paths (e.g., C:\Backups\, D:\Archives\).Scenario: A security team performs a manual red team exercise or internal penetration test, using vaska to encrypt test payloads or staging data on a non-production host.
RedTeam_Staff, PenTest_Environment) or exclude processes running under user accounts with specific naming conventions (e.g., rt_, pentest_) in non-production domains.Scenario: A legacy application or custom internal tool bundles vaska as a helper executable for local data obfuscation, running it as a child process of the main application service.