ThreatFox: Formbook IOCs

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging Formbook malware to stealthily exfiltrate credentials and browser data through encrypted channels following initial compromise via phishing or exploit kits. Proactive hunting in Azure Sentinel is critical to identify subtle indicators of process injection and anomalous outbound traffic that may evade standard signature-based detection, thereby preventing the silent loss of sensitive organizational information.

IOC Summary

Malware Family: Formbook Total IOCs: 3 IOC Types: sha256_hash, sha1_hash, md5_hash

Type	Value	Threat Type	First Seen	Confidence
sha256_hash	`06fe9a22b45bfa76d0d8ae47a98525701494e47beae12cb13bca3dbf3b626315`	payload	2026-08-14	95%
sha1_hash	`b511b3d773d5755c0d156fa17c8cd92d55d3873f`	payload	2026-08-14	95%
md5_hash	`c7c613a0bd28cc5b344d21e16c0d1f58`	payload	2026-08-14	95%

KQL: Hash Hunt

// Hunt for files matching known malicious hashes
// Source: ThreatFox - Formbook
let malicious_hashes = dynamic(["06fe9a22b45bfa76d0d8ae47a98525701494e47beae12cb13bca3dbf3b626315", "b511b3d773d5755c0d156fa17c8cd92d55d3873f", "c7c613a0bd28cc5b344d21e16c0d1f58"]);
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 — Formbook

False Positive Guidance

Here are 5 specific false positive scenarios and corresponding exclusion strategies for the ThreatFox: Formbook IOCs detection rule:

Legitimate Browser Auto-Update Traffic
- Scenario: Modern enterprise browsers (e.g., Microsoft Edge, Google Chrome) frequently initiate encrypted outbound connections to their update servers (*.google.com, *.microsoft.com) to download patches or sync configuration data. If the Formbook rule monitors for “unusual outbound traffic” on standard ports (443), these routine updates may trigger alerts due to high-volume data transfer resembling exfiltration patterns.
- Filter/Exclusion: Exclude network flows where the destination IP belongs to known browser update CDNs and the source process is msedge.exe or chrome.exe. Add a filter: AND (Destination.Domain IN ["*.google.com", "*.microsoft.com"]) AND (Source.Process.Name IN ["msedge.exe", "chrome.exe"]).
Scheduled Credential Backup Jobs
- Scenario: Enterprise Identity Management tools like Microsoft Active Directory Federation Services (ADFS) or Okta often run scheduled jobs to back up credential stores or sync user data. These tasks involve reading large volumes of sensitive data and transmitting it over encrypted channels, which mimics the behavior of Formbook exfiltrating credentials.
- Filter/Exclusion: Create an exclusion for processes running under specific service accounts (e.g., NT SERVICE\ADFS, OktaSyncService) during known maintenance windows. Filter logic: AND (Source.User IN ["DOMAIN\BackupSvc", "DOMAIN\IdentityAdmin"]) AND (Time BETWEEN [02:00, 04:00]).
Phishing Simulation Platform Scans
- Scenario: Security teams often deploy tools like KnowBe4, Proofpoint Essentials, or Coveware