The CryptoPP modulo detection rule identifies potential cryptographic library usage that may indicate obfuscation or data manipulation by adversaries. SOC teams should proactively hunt for this behavior in Azure Sentinel to uncover covert communication or data exfiltration techniques that evade traditional detection methods.
YARA Rule
rule CryptoPP_modulo
{ meta:
author = "Maxx"
description = "CryptoPP modulo"
strings:
$c0 = { 83 EC 20 53 55 8B 6C 24 2C 8B D9 85 ED 89 5C 24 08 75 18 8D 4C 24 0C E8 ?? ?? ?? ?? 8D 44 24 0C 68 ?? ?? ?? ?? 50 E8 ?? ?? ?? ?? 8D 4D FF 56 85 CD 57 75 09 8B 53 04 8B 02 23 C1 EB 76 8B CB E8 ?? ?? ?? ?? 83 FD 05 8B C8 77 2D 33 F6 33 FF 49 85 C0 74 18 8B 53 04 8D 41 01 8D 14 8A 8B 0A 03 F1 83 D7 00 48 83 EA 04 85 C0 77 F1 6A 00 55 57 56 E8 ?? ?? ?? ?? EB 3B 33 C0 8B D1 49 85 D2 74 32 8B 54 24 10 33 DB 8D 71 01 8B 52 04 8D 3C 8A 8B 17 33 ED 0B C5 8B 6C 24 34 33 C9 53 0B CA 55 }
$c1 = { 6A FF 68 ?? ?? ?? ?? 64 A1 00 00 00 00 50 64 89 25 00 00 00 00 83 EC 2C 56 57 8B F1 33 FF 8D 4C 24 20 89 7C 24 08 E8 ?? ?? ?? ?? 8D 4C 24 0C 89 7C 24 3C E8 ?? ?? ?? ?? 8B 44 24 48 8D 4C 24 0C 50 56 8D 54 24 28 51 52 C6 44 24 4C 01 E8 ?? ?? ?? ?? 8B 74 24 54 83 C4 10 8D 44 24 20 8B CE 50 E8 ?? ?? ?? ?? 8B 7C 24 18 8B 4C 24 14 8B D7 33 C0 F3 AB 52 E8 ?? ?? ?? ?? 8B 7C 24 30 8B 4C 24 2C 8B D7 33 C0 C7 44 24 10 ?? ?? ?? ?? 52 F3 AB E8 ?? ?? ?? ?? 8B 4C 24 3C 83 C4 08 8B C6 64 89 }
$c2 = { 83 EC 24 53 55 8B 6C 24 30 8B D9 85 ED 89 5C 24 08 75 18 8D 4C 24 0C E8 ?? ?? ?? ?? 8D 44 24 0C 68 ?? ?? ?? ?? 50 E8 ?? ?? ?? ?? 8D 4D FF 56 85 CD 57 75 09 8B 53 0C 8B 02 23 C1 EB 76 8B CB E8 ?? ?? ?? ?? 83 FD 05 8B C8 77 2D 33 F6 33 FF 49 85 C0 74 18 8B 53 0C 8D 41 01 8D 14 8A 8B 0A 03 F1 83 D7 00 48 83 EA 04 85 C0 77 F1 6A 00 55 57 56 E8 ?? ?? ?? ?? EB 3B 33 C0 8B D1 49 85 D2 74 32 8B 54 24 10 33 DB 8D 71 01 8B 52 0C 8D 3C 8A 8B 17 33 ED 0B C5 8B 6C 24 38 33 C9 53 0B CA 55 }
$c3 = { 6A FF 68 ?? ?? ?? ?? 64 A1 00 00 00 00 50 64 89 25 00 00 00 00 83 EC 1C 56 57 8B F1 33 FF 8D 4C 24 0C 89 7C 24 08 E8 ?? ?? ?? ?? 8D 4C 24 18 89 7C 24 2C E8 ?? ?? ?? ?? 8B 44 24 38 8D 4C 24 18 50 56 8D 54 24 14 51 52 C6 44 24 3C 01 E8 ?? ?? ?? ?? 8B 74 24 44 83 C4 10 8D 44 24 0C 8B CE 50 E8 ?? ?? ?? ?? 8B 4C 24 18 8B 7C 24 1C 33 C0 F3 AB 8B 4C 24 1C 51 E8 ?? ?? ?? ?? 8B 4C 24 10 8B 7C 24 14 33 C0 F3 AB 8B 54 24 14 52 E8 ?? ?? ?? ?? 8B 4C 24 2C 83 C4 08 8B C6 64 89 0D 00 00 00 }
condition:
any of them
}This YARA rule can be deployed in the following contexts:
This rule contains 4 string patterns in its detection logic.
Scenario: System update or patching using sudo apt or yum
Filter/Exclusion: Check for command-line arguments like --upgrade, --dist-upgrade, or --fix-broken in the command line.
Example Filter: process.command_line contains "--upgrade" or "apt upgrade" or "yum update"
Scenario: Scheduled backup job using rsync or tar
Filter/Exclusion: Filter out processes associated with backup tools like rsync, tar, or backup in the command line.
Example Filter: process.name in ("rsync", "tar") or process.command_line contains "backup"
Scenario: Administrative task using sudo to configure system settings
Filter/Exclusion: Exclude processes initiated with sudo that are part of routine administrative tasks.
Example Filter: process.command_line contains "sudo" and process.parent_process.name == "bash"
Scenario: Log rotation or system logging using logrotate
Filter/Exclusion: Identify and exclude processes related to log rotation tools like logrotate or rsyslog.
Example Filter: process.name == "logrotate" or process.command_line contains "logrotate"
Scenario: Cryptographic operations in legitimate security tools like OpenSSL or GnuPG
Filter/Exclusion: Exclude processes using cryptographic libraries or tools such as openssl, gpg, or ssh.
Example Filter: process.name in ("openssl", "gpg", "ssh") or process.command_line contains "openssl" or "gpg"