Usteal

rule MALWARE_WIN_USTEAL_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Usteal"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "usteal" ascii wide nocase
        $s2 = "trojan-psw.win32.usteal" ascii wide nocase
        $s3 = "pws:win32/usteal" ascii wide nocase
        $s4 = "trojan:win32/usteal" ascii wide nocase
        $s5 = "win32/usteal" ascii wide nocase
        $s6 = "trojan.usteal" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Usteal (Infostealer) Execution & Triage
id: 6cca5823-5371-52a2-8b81-660127d14cf8
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Usteal malware family. Detects browser credential database harvesting,
  master key queries, and DPAPI extraction routines typical of modern infostealers.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/usteal
- https://malware-families-catalog.systemhelpdesk.com/defensive/infostealer-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.infostealer
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1555_003
- attack.t1555_004
- attack.t1052_001
- attack.t1041
- attack.t1082
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \cmd.exe
    - \powershell.exe
    - \rundll32.exe
    CommandLine|contains:
    - \Google\Chrome\User Data\Default\Login Data
    - \AppData\Roaming\Mozilla\Firefox\Profiles
    - \AppData\Local\Microsoft\Edge\User Data
    - vaultcmd.exe /list
    - dpapi
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: high

rule MALWARE_WIN_USTEAL_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Usteal tradecraft"
        tier = "T3 - Attribution Fingerprint"
        confidence = "High (Confirmed Family Signature)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        // Core family identifier & heuristic payload signatures
        $attrib_str = "usteal" ascii wide nocase
        $pe_magic = "MZ" ascii
        $net_marker = "http" ascii nocase
    condition:
        uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}