ThreatFox: ACR Stealer IOCs

Hunt Hypothesis

This hunt targets adversary behavior involving the deployment of ACR Stealer malware by searching for specific indicators of compromise across endpoints and network logs to identify active credential theft operations. Proactively hunting for these six IOCs within Azure Sentinel is critical to rapidly detect and contain early-stage data exfiltration attempts before they escalate into broader lateral movement incidents.

IOC Summary

Malware Family: ACR Stealer Total IOCs: 6 IOC Types: md5_hash, sha1_hash, sha256_hash

Type	Value	Threat Type	First Seen	Confidence
md5_hash	`778aad49c1279d5a647759894155d40a`	payload	2026-07-18	95%
sha256_hash	`b2ab8825b84e6f0209cf713dcf7156c93ae82f37a6d9f0ca9072e228825c8d63`	payload	2026-07-18	95%
sha1_hash	`54fbaa90e47e9ea04deebb6dd2a5e8ed48e86a35`	payload	2026-07-18	95%
sha256_hash	`31cf473bb93abef0760d4992d45bafcd936edb7c26193c175f8491f8ffaef0e0`	payload	2026-07-18	95%
sha1_hash	`1d17d0e432e085af891afabedafaf9c1f1b3993f`	payload	2026-07-18	95%
md5_hash	`d1e5cbeac0e02e97a34aca7c9c54db5c`	payload	2026-07-18	95%

KQL: Hash Hunt

// Hunt for files matching known malicious hashes
// Source: ThreatFox - ACR Stealer
let malicious_hashes = dynamic(["778aad49c1279d5a647759894155d40a", "b2ab8825b84e6f0209cf713dcf7156c93ae82f37a6d9f0ca9072e228825c8d63", "54fbaa90e47e9ea04deebb6dd2a5e8ed48e86a35", "31cf473bb93abef0760d4992d45bafcd936edb7c26193c175f8491f8ffaef0e0", "1d17d0e432e085af891afabedafaf9c1f1b3993f", "d1e5cbeac0e02e97a34aca7c9c54db5c"]);
DeviceFileEvents
| where SHA256 in (malicious_hashes) or SHA1 in (malicious_hashes) or MD5 in (malicious_hashes)
| project Timestamp, DeviceName, FileName, FolderPath, SHA256, InitiatingProcessFileName
| order by Timestamp desc

Required Data Sources

Sentinel Table	Notes
`DeviceFileEvents`	Ensure this data connector is enabled

References

ThreatFox — ACR Stealer

False Positive Guidance

Here are 5 specific false positive scenarios for the ThreatFox: ACR Stealer IOCs detection rule, tailored for an enterprise environment:

Endpoint Protection Scanning of Quarantine Archives
- Scenario: The organization’s EDR (e.g., CrowdStrike Falcon or Microsoft Defender for Endpoint) performs a scheduled deep scan of the C:\ProgramData\Quarantine directory. This directory contains archived logs and previous malware samples that match the ACR Stealer hash signatures but are benign historical artifacts rather than active threats.
- Filter/Exclusion: Create an exclusion rule to ignore alerts where the process path is within the EDR’s quarantine or archive directories (e.g., *\Quarantine\*, *\ThreatHistory\*) and the file age exceeds 30 days.
Software Deployment via SCCM or Intune
- Scenario: During a monthly patch cycle, the System Center Configuration Manager (SCCM) or Microsoft Intune agent pushes an update package containing a legitimate software installer that includes a shared library or dependency with a hash matching one of the ACR Stealer IOCs. The deployment job executes as a scheduled task (Task Scheduler) running under the SYSTEM account.
- Filter/Exclusion: Exclude alerts where the parent process is the Software Update Agent (e.g., ccmexec.exe, MicrosoftEdgeUpdate.exe) or the user context is NT AUTHORITY\SYSTEM during known maintenance windows (e.g., 02:00–04:00 UTC).
Security Information and Event Management (SIEM) Log Ingestion
- Scenario: The SIEM platform (e.g., Splunk or Sentinel) ingests raw log files from legacy network appliances. A specific log parser script processes these files, temporarily extracting a configuration file that