ThreatFox: Formbook IOCs

Hunt Hypothesis

This hypothesis targets the presence of Formbook malware, a high-severity data-stealer that exfiltrates credentials and banking details through memory injection and encrypted C2 communications. Proactively hunting for these IOCs in Azure Sentinel is critical to identify compromised endpoints early, as the malware often enters via phishing and operates stealthily to steal sensitive information before detection.

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	`210ae656df91ca6fe5cca2c03f737716637537e6b8d9e0476bafc268ceb64c32`	payload	2026-09-10	95%
sha1_hash	`0b3e8e11ac0aa3b88ea280af0b6625fabde3f8ad`	payload	2026-09-10	95%
md5_hash	`8594a6fe0265fa1629c16411f0fd3d77`	payload	2026-09-10	95%

KQL: Hash Hunt

// Hunt for files matching known malicious hashes
// Source: ThreatFox - Formbook
let malicious_hashes = dynamic(["210ae656df91ca6fe5cca2c03f737716637537e6b8d9e0476bafc268ceb64c32", "0b3e8e11ac0aa3b88ea280af0b6625fabde3f8ad", "8594a6fe0265fa1629c16411f0fd3d77"]);
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

Scenario: A security team deploys a YARA scanner (e.g., ClamAV or a custom YARA engine) to audit the file system for known Formbook signatures. The scanner loads the IOCs into memory and executes a lightweight analysis routine, triggering the detection logic which identifies the characteristic memory injection patterns or encrypted C2 communication stubs as active malware.
- Filter/Exclusion: Exclude processes where the parent process is a known scanning tool (e.g., clamd, yara, osqueryd) or where the execution context is within a dedicated security tooling directory (e.g., C:\Program Files\SecurityTools\).
Scenario: An IT administrator runs a scheduled PowerShell script to validate network connectivity to a staging server that mimics the Formbook C2 protocol for testing purposes. The script uses Invoke-WebRequest or Net.WebClient to send encrypted payloads to a test endpoint, matching the rule’s criteria for encrypted outbound communication and memory-based data handling.
- Filter/Exclusion: Exclude network connections where the destination IP is within the internal staging subnet (e.g., 10.20.0.0/24) or where the source process is powershell.exe and the command line contains specific test identifiers (e.g., -TestFormbookC2).
Scenario: A developer uses a memory debugging tool like WinDbg or x64dbg to analyze a captured sample of Formbook for reverse engineering. The debugger injects code into the target process to inspect memory structures, creating a pattern that closely resembles the malware’s memory injection and data exfiltration behavior.
- Filter/Exclusion: Exclude events where the parent process is a known debugger (e.g., windbg.exe, x64dbg.exe, ida64.exe) or where the process tree includes a development