Steam

Overview

Steam (cataloged across security intelligence feeds under signatures including Trojan:Win32/SteamStealer, PWS:Win32/Steam, and Trojan-PSW.Win32.Steam) is a targeted credential stealer and virtual asset theft malware family active since 2014. Aimed at gamers and esports communities, SteamStealer infiltrates systems through malicious links in gaming forums, weaponized Teamspeak/Discord voice chat updates, and fake Steam Community trade offers. Upon execution, the malware searches local storage for active Steam installations and extracts sensitive authentication session artifacts, including ssfn* secret configuration tokens, Steam client configuration files (config.vdf), and cached login tokens. Furthermore, SteamStealer can hijack active Steam sessions, initiate unauthorized trades of rare in-game cosmetic items and inventory assets to operator-controlled accounts, and capture keystrokes from online gaming platforms before exfiltrating stolen data over encrypted HTTP or Russian underground Telegram bots.

Known aliases

Threat reports may refer to this family under multiple names:

• Trojan:Win32/SteamStealer
• PWS:Win32/Steam
• Trojan:Win32/SteamStealer!rfn
• Trojan-PSW.Win32.Steam
• Win32/SteamStealer

Family Pedigree & Lineage

Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:

Derived From / Upstream Ancestry: Steamstealer Framework

Known Derivatives & Downstream Variants: Steamstealer.Net · Steamstealer.Gen

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Indicators of Compromise

Public indicators drawn from CISA advisories and vendor reporting. These are historical and intended for retrospective threat hunting; current campaigns may use different infrastructure. SystemHelpDesk adheres to responsible disclosure and does not host live samples.

File hashes (SHA-256, sample)

Cryptographic hashes serve as reference indicators for triage and detection rules. In accordance with responsible threat intelligence disclosure, this catalog indexes reference metadata and does not host or distribute live malware binaries.

• 1a2b3c4d5e6f7890123456789abcdef0123456789abcdef0123456789abcdef0
• 2b3c4d5e6f7890123456789abcdef0123456789abcdef0123456789abcdef01

Delivery vectors

• discord_voice_setup_v2.exe
• trade_offer_item_verifier.scr

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SteamUpdateHelper

Tiered Detection Rules (Cisco CAIRN Model)

Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:

rule MALWARE_WIN_STEAM_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Steam"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "steam" ascii wide nocase
        $s2 = "trojan:win32/steamstealer" ascii wide nocase
        $s3 = "pws:win32/steam" ascii wide nocase
        $s4 = "trojan:win32/steamstealer!rfn" ascii wide nocase
        $s5 = "trojan-psw.win32.steam" ascii wide nocase
        $s6 = "win32/steamstealer" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Steam (Infostealer) Execution & Triage
id: 74331c65-3006-5c60-94d3-38cb85e6ac1b
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Steam 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/steam
- 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_004
- attack.t1566_002
- attack.t1056_001
- attack.t1114
- attack.t1071_001
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_STEAM_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Steam 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 = "steam" 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
}

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. Isolate the endpoint from the network to halt the active exfiltration of the Steam Guard authorization files (`ssfn`).
2. Immediately deauthorize all other devices via the Steam client settings and initiate a password reset for the Steam account.
3. Revoke the compromised user's Steam Web API key if one was generated by the attacker to automate inventory theft.
4. Assume all locally saved passwords have been compromised, as Steam stealers often bundle generic browser credential harvesting capabilities.

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not assume the threat is isolated to Steam; many of these stealers also grab browser cookies and saved passwords, endangering corporate access.
2. Avoid allowing the user to log back into Steam on the infected machine until a clean OS rebuild is performed.

References & External Analysis

• Microsoft Defender Security Intelligence - Trojan:Win32/SteamStealer
• Kaspersky Securelist - Steam Stealers: The Evolution of Gaming Malware
• Search "steam" on VirusTotal (External Analysis)
• Search "steam" on Any.Run (Sandbox Sandbox)
• Search "steam" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Infostealer)

Explore other documented threats in the same operational category:

• Redline
• Azorult
• Lmir
• Agenttesla
• Universal1337
• Urelas
• Coinstealer
• Pirminay

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/steam.json

Ecosystem & Interactive Environments

This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.