This hypothesis targets the presence of the PiCryptor ransomware variant, which encrypts files and appends a specific extension to extort victims. Proactively hunting for this signature allows the SOC to identify early-stage infections or dormant payloads within Azure Sentinel, enabling rapid isolation before widespread data encryption occurs.
rule PiCryptor10byScofield
{
meta:
author="malware-lu"
strings:
$a0 = { 55 8B EC 83 C4 EC 53 56 57 31 C0 89 45 EC B8 40 1E 06 00 E8 48 FA FF FF 33 C0 55 68 36 1F 06 00 64 FF 30 64 89 20 6A 00 68 80 00 00 00 6A 03 6A 00 6A 01 68 00 00 00 80 8D 55 EC 31 C0 E8 4E F4 FF FF 8B 45 EC E8 F6 F7 FF FF 50 E8 CC FA FF FF 8B D8 83 FB FF 74 4E 6A 00 53 E8 CD FA FF FF 8B F8 81 EF AC 26 00 00 6A 00 6A 00 68 AC 26 00 00 53 E8 DE FA FF FF 89 F8 E8 E3 F1 FF FF 89 C6 6A 00 68 28 31 06 00 57 56 53 E8 AE FA FF FF 53 E8 80 FA FF FF 89 FA 81 EA 72 01 00 00 8B C6 E8 55 FE FF FF 89 C6 89 F0 09 C0 74 05 E8 A8 FB FF FF 31 C0 }
$a1 = { 55 8B EC 83 C4 EC 53 56 57 31 C0 89 45 EC B8 40 1E 06 00 E8 48 FA FF FF 33 C0 55 68 36 1F 06 00 64 FF 30 64 89 20 6A 00 68 80 00 00 00 6A 03 6A 00 6A 01 68 00 00 00 80 8D 55 EC 31 C0 E8 4E F4 FF FF 8B 45 EC E8 F6 F7 FF FF 50 E8 CC FA FF FF 8B D8 83 FB FF 74 4E 6A 00 53 E8 CD FA FF FF 8B F8 81 EF AC 26 00 00 6A 00 6A 00 68 AC 26 00 00 53 E8 DE FA FF FF 89 F8 E8 E3 F1 FF FF 89 C6 6A 00 68 28 31 06 00 57 56 53 E8 AE FA FF FF 53 E8 80 FA FF FF 89 FA 81 EA 72 01 00 00 8B C6 E8 55 FE FF FF 89 C6 89 F0 09 C0 74 05 E8 A8 FB FF FF 31 C0 5A 59 59 64 89 10 68 3D 1F 06 00 8D 45 EC E8 C3 F6 FF FF C3 }
$a2 = { 89 55 F8 BB 01 00 00 00 8A 04 1F 24 0F 8B 55 FC 8A 14 32 80 E2 0F 32 C2 8A 14 1F 80 E2 F0 02 D0 88 14 1F 46 8D 45 F4 8B 55 FC E8 [4] 8B 45 F4 E8 [4] 3B F0 7E 05 BE 01 00 00 00 43 FF 4D F8 75 C2 [4] 5A 59 59 64 89 10 68 [4] 8D 45 F4 E8 [4] C3 E9 }
condition:
$a0 or $a1 at pe.entry_point or $a2
}This YARA rule can be deployed in the following contexts:
This rule contains 3 string patterns in its detection logic.
Scenario: A developer or operations engineer runs a local build pipeline or CI/CD agent (e.g., Jenkins, GitLab Runner, or Azure DevOps) that compiles C/C++ code using gcc or clang. The resulting executable or intermediate object files may contain specific byte sequences or entropy patterns that match the generic heuristic of the PiCryptor10byScofield YARA rule, especially if the build artifacts are not stripped of debug symbols or if the compiler generates predictable padding.
gcc, clang, make, or ninja, or exclude file paths under standard build directories such as /tmp/build/, C:\Users\<user>\AppData\Local\Temp\, or *.o/*.obj file extensions.Scenario: An administrator performs a manual backup or archival task using 7-Zip (7z.exe) or tar to compress a large directory of source code or configuration files into a .7z or .tar.gz archive. The compression algorithm (LZMA or Deflate) can create high-entropy blocks that mimic the encrypted payload structure targeted by the PiCryptor heuristic, particularly if the archive contains many small, random-looking files.
7z.exe, 7za.exe, tar.exe, or gzip.exe, and where the file extension is .7z, .tar, .gz, or .zip. Additionally, exclude paths containing keywords like backup, archive, or snapshot.Scenario: A security team or application developer uses a tool like Frida, x64dbg, or Ghidra to perform dynamic analysis or reverse engineering on a benign application. These tools often inject code or