Adversaries may use CRC32 hash values to obfuscate or manipulate data during exfiltration or persistence. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify potential data tampering or covert communication channels.
YARA Rule
rule CRC32_poly_Constant {
meta:
author = "_pusher_"
description = "Look for CRC32 [poly]"
date = "2015-05"
version = "0.1"
strings:
$c0 = { 2083B8ED }
condition:
$c0
}
This YARA rule can be deployed in the following contexts:
This rule contains 1 string patterns in its detection logic.
Scenario: A system update or patching tool calculates CRC32 hashes for integrity checks.
Filter/Exclusion: Exclude processes related to known update tools (e.g., Windows Update, Chocolatey, Ansible, Puppet) by checking the process name or command line arguments.
Scenario: A backup or archive tool (e.g., rsync, tar, 7z, Veeam) computes CRC32 hashes during data compression or transfer.
Filter/Exclusion: Exclude processes associated with backup tools by matching the process name or using a whitelist of known backup utilities.
Scenario: A scheduled system maintenance task (e.g., Task Scheduler, cron job) runs a script that calculates CRC32 for file verification.
Filter/Exclusion: Exclude tasks with known scheduled job names or user accounts (e.g., SYSTEM, LocalService) and filter based on the command line or script path.
Scenario: A network monitoring tool (e.g., Wireshark, tcpdump, Nmap) captures and processes CRC32 checksums in network packets.
Filter/Exclusion: Exclude network-related processes by checking the process name or using a filter on the source/destination IP or port.
Scenario: A database or application performs CRC32 calculations for data integrity during replication or synchronization.
Filter/Exclusion: Exclude database processes (e.g., MySQL, PostgreSQL, SQL Server) or application-specific processes by matching the process name or user context.