Yunsip

Overview

Yunsip (tracked across security vendor definitions as PWS:Win32/Yunsip, Trojan:Win32/Yunsip, and PWS:Win32/Yunsip.A) is an aggressive credential-stealing trojan and secondary loader targeting Windows endpoints since 2013. Designed to harvest authentication material from infected workstations, Yunsip systematically scans web browser data stores (including Google Chrome, Mozilla Firefox, and Internet Explorer/Edge), email clients, and FTP configuration files to locate saved passwords, session cookies, and user autofill databases. In addition to credential extraction, Yunsip establishes persistent communication with remote command-and-control servers over HTTP/HTTPS, enabling attackers to deploy secondary malware payloads such as keyloggers, remote access backdoors, or cryptominers. The malware achieves persistence by creating autostart registry entries under HKCU\Software\Microsoft\Windows\CurrentVersion\Run and registering scheduled tasks disguised as legitimate Windows update services.

Known aliases

Threat reports may refer to this family under multiple names:

• PWS:Win32/Yunsip
• Trojan:Win32/Yunsip
• PWS:Win32/Yunsip.A
• Trojan.Yunsip
• Win32/Yunsip

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: Win32 Credential Stealer Family

Known Derivatives & Downstream Variants: Yunsip.A · Yunsip.B · Yunsip.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:

• T1056.001: Implement Endpoint Detection and Response (EDR) to monitor for suspicious API calls related to keystroke interception. Enforce Multi-Factor Authentication (MFA) to render stolen passwords useless.
• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.

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.

• a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2
• 3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e

Delivery vectors

• Malicious email attachments disguised as electronic bills and shipment notices
• Compromised software distribution portals bundling trojanized installers

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\YunsipAgent
• %APPDATA%\Microsoft\Yunsip\yunsip_svc.exe

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_YUNSIP_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Yunsip"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "yunsip" ascii wide nocase
        $s2 = "pws:win32/yunsip" ascii wide nocase
        $s3 = "trojan:win32/yunsip" ascii wide nocase
        $s4 = "pws:win32/yunsip.a" ascii wide nocase
        $s5 = "trojan.yunsip" ascii wide nocase
        $s6 = "win32/yunsip" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Yunsip (Infostealer) Execution & Triage
id: b3c959ad-f644-5249-b248-fbbc07eacd34
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Yunsip 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/yunsip
- 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.t1056_001
- attack.t1547_001
- attack.t1071_001
- attack.t1027
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_YUNSIP_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Yunsip 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 = "yunsip" 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. Disconnect the affected host from corporate networks immediately to halt credential exfiltration.
2. Identify and kill active Yunsip processes running from %APPDATA% or %TEMP% directories.
3. Remove persistence entries under HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Yunsip.
4. Enforce immediate enterprise-wide password rotations for all user and administrative accounts used on the machine.

What to Avoid

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

1. Do not allow users to store unencrypted corporate or banking passwords in web browsers.
2. Avoid opening unverified email attachments purporting to be invoices or delivery documents.

References & External Analysis

• Microsoft Defender Security Intelligence - PWS:Win32/Yunsip
• AlienVault OTX Pulse Intelligence - Yunsip Stealer Activity
• Search "yunsip" on VirusTotal (External Analysis)
• Search "yunsip" on Any.Run (Sandbox Sandbox)
• Search "yunsip" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Infostealer)

Explore other documented threats in the same operational category:

• Lynx
• Spytector
• Lumma
• Ardamax
• Lmir
• Pirminay
• Cardspy
• Ribaj

Machine-readable

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