Quasar

Overview

Quasar (broadly tracked as Quasar RAT, QuasarRAT, Backdoor:MSIL/Quasar, and Trojan.MSIL.Quasar) is a high-performance open-source remote access trojan (RAT) developed in C# (.NET) and publicly hosted on GitHub under an MIT license. Originally intended by its creator as a lightweight remote management and systems administration tool, Quasar was swiftly co-opted, modified, and weaponized by commercial cybercriminals and sophisticated nation-state advanced persistent threat (APT) groups. Notable state-sponsored threat actors utilizing custom variants of Quasar include APT10 (Stone Panda, MenuPass), APT33 (Elfin), the Syrian Electronic Army, and the Lazarus Group. Quasar operates over TCP/IP socket connections utilizing TLS-encrypted command-and-control streams, providing operators with a robust suite of remote management and surveillance features. Its capabilities include full reverse desktop remote control (Reverse RDP), SOCKS5 reverse proxy tunneling, real-time keystroke logging via SetWindowsHookEx, webcam and microphone capture, audio recording, interactive remote command shell execution (cmd.exe and PowerShell), process injection and termination, file upload and download, and registry manipulation. Cyber threat actors frequently deploy Quasar using weaponized phishing attachments delivering malicious Word documents exploiting equation editor vulnerabilities (CVE-2017-11882) or archived LNK shortcuts. Once executed, the initial stager utilizes process hollowing (T1055.012) to inject the compiled .NET assembly directly into legitimate Windows processes such as InstallUtil.exe, RegSvcs.exe, or MSBuild.exe to evade traditional signature-based antivirus solutions. In October 2018, CISA released Advisory AA18-337A warning organizations that nation-state cyber actors were routinely weaponizing open-source tools like Quasar RAT against critical infrastructure.

Known aliases

Threat reports may refer to this family under multiple names:

• QuasarRAT
• Backdoor:MSIL/Quasar
• Trojan.MSIL.Quasar
• Win32/Quasar.RAT
• Quasar Client
• Quasar Remote Administration Tool

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: Quasar_Client_Github

Known Derivatives & Downstream Variants: Quasar_V1.3 · Quasar_V1.4 · Cinedoor · Apt10_Quasar_Fork

MITRE ATT&CK Techniques

This family has been observed using the following ATT&CK techniques: T1056.001 · T1113 · T1125 · T1123 · T1059.003 · T1071.001 · T1547.001 · T1555.003 · T1105 · T1055.012 · T1090.001

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.
• T1059.003: Restrict execution of Windows Command Shell (cmd.exe) and block unauthorized batch scripts.
• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.
• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.
• T1113: Monitor for frequent or unauthorized screen captures or clipboard reads. Restrict background applications from accessing desktop APIs.
• T1125: Restrict access to local camera or microphone APIs. Utilize endpoint protection that monitors hardware access.

MITRE D3FEND™ Defensive Countermeasures

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

Exploited Vulnerabilities (CVEs)

This malware family is documented weaponizing the following common vulnerabilities and exposures:

• CVE-2017-11882 — In-depth exploitation analysis and catalog intelligence (NIST NVD ↗).
• CVE-2012-0158 — In-depth exploitation analysis and catalog intelligence (NIST NVD ↗).

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.

• 5b508f72a4209bf26efba098b671a52028ddc87c14a22ad31737be70d8a57102
• a172776c59b67195721118182969b761a17387f5df2307ef086915091219b671
• 2b6a5db21d00f7e44a42e5d7db69b466ea2084c55bc66c5d1e2e1329c31b312b

Delivery vectors

• Spear-phishing emails containing malicious Office documents exploiting formula editor flaw CVE-2017-11882
• ISO or RAR archive attachments containing weaponized LNK shortcuts executing PowerShell
• Staged multi-stage loaders dropping obfuscated .NET assemblies into user profile directories

Persistence mechanisms

• Scheduled task creation executing with highest privileges via schtasks /create /sc onlogon
• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Quasar Client
• Process hollowing into trusted Windows utilities: InstallUtil.exe, RegSvcs.exe, or MSBuild.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_QUASAR_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Quasar"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "quasar" ascii wide nocase
        $s2 = "quasarrat" ascii wide nocase
        $s3 = "backdoor:msil/quasar" ascii wide nocase
        $s4 = "trojan.msil.quasar" ascii wide nocase
        $s5 = "win32/quasar.rat" ascii wide nocase
        $s6 = "quasar client" ascii wide nocase
        $s7 = "quasar remote administration tool" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Quasar (Rat) Execution & Triage
id: efbad2a6-f5d1-5b98-a177-aaecc9356ff8
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Quasar malware family. Detects unauthorized persistence creation via Windows
  Registry Run keys, scheduled tasks, and privilege escalation indicative of RAT installations.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/quasar
- https://malware-families-catalog.systemhelpdesk.com/defensive/backdoor-rat-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.rat
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1056_001
- attack.t1113
- attack.t1125
- attack.t1123
- attack.t1059_003
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \reg.exe
    - \schtasks.exe
    - \cmd.exe
    - \powershell.exe
    CommandLine|contains:
    - \CurrentVersion\Run
    - /create /tn
    - bypass -enc
    - net user /add
    - net localgroup administrators
  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_QUASAR_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Quasar 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 = "quasar" 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
}

References & External Analysis

• CISA Alert AA18-337A: Open Source Tools Weaponized by Threat Actors
• Palo Alto Networks Unit 42: Quasar RAT Profile and APT10 Campaigns
• Mandiant: QuasarRAT In-Memory Evasion and Threat Actor Usage
• CISA Analysis Report AR18-337A: Quasar RAT Technical Architecture
• CISA Advisory: AA18-337A
• Search "quasar" on VirusTotal (External Analysis)
• Search "quasar" on Any.Run (Sandbox Sandbox)
• Search "quasar" on MalwareBazaar (Malware Samples)

North American Authority Advisory (CISA / NIST)

The Cybersecurity and Infrastructure Security Agency (CISA) has published an official US federal advisory on this family, which can be mapped to NIST Cybersecurity Framework (CSF) incident response controls: AA18-337A ↗

Frequently Asked Questions

Related Threats (Category: Rat)

Explore other documented threats in the same operational category:

• Rebhip
• Netwiredrc
• Cosmu
• Beast
• Immirat
• Darkkomet
• Plugx
• Protux

Machine-readable

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