This rule detects the custom hashing algorithm of Lockbit4.0 unpacked

Hunt Hypothesis

This hunt hypothesis targets adversaries executing the unique custom hashing algorithm associated with the LockBit 4.0 ransomware variant to identify early-stage unpacking activities indicative of an active infection. Proactive hunting for this signature in Azure Sentinel is critical because it enables the SOC team to detect and isolate compromised systems before the encryption phase begins, thereby minimizing potential data loss and operational downtime.

YARA Rule

rule mal_lockbit4_hashing_alg_win_feb24
{
    meta:
        author = "0x0d4y"
        description = "This rule detects the custom hashing algorithm of Lockbit4.0 unpacked"
        date = "2024-02-16"
        score = 100
        reference = "https://0x0d4y.blog/lockbit4-0-evasion-tales/"
        hash = "062311F136D83F64497FD81297360CD4"

        id = "e91aedba-6f70-4ca2-9217-2991cbbc6e8d"
        license = "CC BY 4.0"
        rule_matching_tlp = "TLP:WHITE"
        rule_sharing_tlp = "TLP:WHITE"
        malpedia_family = "win.lockbit"
    strings:
        $hashing_alg = { 41 89 d0 46 0f be 04 00 45 09 c0 74 ?? 45 8d 48 ?? 45 8d 50 ?? 41 80 f9 ?? 45 0f 43 d0 44 31 d1 44 8d 04 3a 45 0f af c2 41 01 c8 89 d1 31 f9 09 d2 0f 44 ca 41 0f af c8 44 01 d1 ff c2 eb ?? 49 ff c6 }
        
    condition:
        uint16(0) == 0x5a4d and
        $hashing_alg
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

References

• https://0x0d4y.blog/lockbit4-0-evasion-tales/
• Source Rule

False Positive Guidance

Here are 3-5 specific false positive scenarios for the Lockbit4.0 Unpacked Custom Hashing Algorithm detection rule, including suggested filters and exclusions:

• Scenario: Enterprise Backup Software Performing Integrity Checks

  • Context: Legacy or modern backup solutions (e.g., Veeam Backup & Replication, Commvault, or Rubrik) often utilize custom hashing routines to verify file integrity during the “unpacked” phase of a restore job or pre-backup scan. These tools may generate binary structures that mimic the specific entropy and byte patterns of Lockbit’s custom hash, triggering the rule when processing large archive files (.vbk, .cva).
  • Suggested Filter/Exclusion: Exclude processes running under the service accounts for these backup agents (e.g., VeeamAgent.exe, commvault_service.exe) from the detection scope. Additionally, filter out events where the parent process is a known backup scheduler (e.g., vssvc.exe or Task Scheduler triggering vbragent64.exe).

• Scenario: Antivirus/EDR Deep Scan of Compressed Archives

  • Context: Security suites like CrowdStrike Falcon, Microsoft Defender for Endpoint, or Symantec Endpoint Protection frequently unpack and scan .zip, .7z, or .tar archives during real-time protection. When these tools extract nested archives, their internal decompression engines may utilize a hashing mechanism that shares statistical similarities with Lockbit4.0’s algorithm, causing the rule to fire on legitimate file extraction events.
  • Suggested Filter/Exclusion: Create an exclusion for the specific EDR agent process names (e.g., Cnsys.exe, MsMpEng.exe, Rtvscan64.exe). Furthermore, add a filter to ignore detections where the file extension is `.zip