ThreatFox: ACR Stealer IOCs

Hunt Hypothesis

This hunt hypothesis targets adversary behavior where ACR Stealer malware infiltrates endpoints through phishing vectors to exfiltrate critical browser credentials and authentication data. Proactively hunting for these indicators in Azure Sentinel is essential due to the high severity of credential theft, which often serves as a precursor to lateral movement and broader identity compromise within the organization.

IOC Summary

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

Type	Value	Threat Type	First Seen	Confidence
sha256_hash	`105195dfdfbfdce7cf13f50d92bba761eba5bc22c31000109a67708f61474e12`	payload	2026-08-28	95%
sha1_hash	`ba655e73a1c08143324ffeaf56b6f6bea0a134e6`	payload	2026-08-28	95%
md5_hash	`8be48ea27f6cd6b2ec2ef3be4977322d`	payload	2026-08-28	95%
md5_hash	`98f00e36daaf4c4bae91031d4b53ea9b`	payload	2026-08-28	95%
sha256_hash	`46ced738ab9a9a37df3e36c6a8603742f26783f0be2fa845bdec10b5ddb50bfb`	payload	2026-08-28	95%
sha1_hash	`6c19930c2b6b2ec49b42399dcd8e477de347c010`	payload	2026-08-28	95%

KQL: Hash Hunt

// Hunt for files matching known malicious hashes
// Source: ThreatFox - ACR Stealer
let malicious_hashes = dynamic(["105195dfdfbfdce7cf13f50d92bba761eba5bc22c31000109a67708f61474e12", "ba655e73a1c08143324ffeaf56b6f6bea0a134e6", "8be48ea27f6cd6b2ec2ef3be4977322d", "98f00e36daaf4c4bae91031d4b53ea9b", "46ced738ab9a9a37df3e36c6a8603742f26783f0be2fa845bdec10b5ddb50bfb", "6c19930c2b6b2ec49b42399dcd8e477de347c010"]);
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 rule, including targeted filters and exclusions suitable for an enterprise environment:

Scenario: Legitimate Browser Credential Sync via Enterprise Management Tools
- Context: Endpoint Detection and Response (EDR) agents or Group Policy scripts often trigger browser credential synchronization processes that mimic the exfiltration behavior of ACR Stealer. For instance, when Microsoft Intune pushes a policy to sync Chrome or Edge passwords across devices, it generates network traffic patterns similar to the malware’s data exfiltration signature.
- Suggested Filter/Exclusion: Create an exclusion rule that filters out events where the parent process is IntuneManagementExtension.exe (or Microsoft.Intune.Management.Extension) and the destination port matches standard enterprise sync ports (e.g., 443, 8080). Additionally, exclude traffic originating from known internal IP ranges of the Identity Provider (e.g., Azure AD B2C endpoints) during business hours.
Scenario: Scheduled Backup Jobs Utilizing Cloud Storage APIs
- Context: Automated backup solutions like Veeam Backup & Replication or Rubrik frequently exfiltrate large volumes of sensitive data to cloud storage buckets (AWS S3, Azure Blob) using API calls that match the “credential and browser data” payload structure detected by ACR Stealer. These jobs often run during off-hours but can overlap with user activity windows.
- Suggested Filter/Exclusion: Implement a time-based exclusion for alerts generated between 01:00 and 05:00 local time when the source process is Veeam.Backup.Service.exe or rubrik-agent. Furthermore, add an IOC exclusion list containing the specific SHA-256 hashes of the backup agents’ executable binaries to prevent