Quasarrat

Overview

QuasarRAT (frequently tracked as Quasar, Quasar Remote Administration Tool, and Backdoor:MSIL/Quasar) is a powerful open-source remote access trojan coded in C# (.NET). While originally published on GitHub by developer 'MaxXor' as an administrative management utility, the software's lightweight architecture, robust TLS encryption, and modular design led to widespread weaponization across cybercrime groups and advanced persistent threat (APT) actors. The implant establishes reverse TCP connections to command-and-control infrastructure using TLS-secured sockets with optional certificate pinning to defeat SSL/TLS inspection proxies. Once connected, Quasar delivers an exhaustive suite of surveillance capabilities: real-time desktop screen streaming, audio capturing, keystroke logging, reverse socks5 proxy routing, file system traversal, remote shell access, and process management. It systematically extracts stored credentials from web browsers (Chrome, Edge, Firefox), FTP clients, and email clients. Multiple government advisories (including CISA Alert AA18-337A) highlight Quasar's deployment by nation-state actors including APT10 and APT33 for long-term target surveillance.

Known aliases

Threat reports may refer to this family under multiple names:

• Quasar RAT
• Quasar
• Backdoor.MSIL.Quasar
• Win32/Quasar

Threat Actor Attribution

Attribution is probabilistic, not a science. Each link below states its confidence level and the evidence behind it.

• APT10, APT33, Gaza Cybergang, Diverse Cybercrime Actors High confidence
  Basis:

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 Open-Source Repository

Known Derivatives & Downstream Variants: Quasar Rat V1.3 · Quasar Rat V1.4 · Custom Apt-Modified Quasar

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.
• T1059.003: Restrict execution of Windows Command Shell (cmd.exe) and block unauthorized batch scripts.
• T1113: Monitor for frequent or unauthorized screen captures or clipboard reads. Restrict background applications from accessing desktop APIs.

MITRE D3FEND™ Defensive Countermeasures

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

Command & Control (C2) and Network Profile

How this family talks to its operators. C2 traffic can often identify a family even when its code and configuration are hard to analyse. Ports and patterns are historical and change between campaigns, so use them as hunting leads rather than block-only rules.

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.

• a4c7e6b0142b6a7a58a7be8e7e1273934d70b6d19a2e31d4512b18972b9a1111
• f7b2c93847849e7552eb412854c6020c644d622830f0f35a4d467888b13d2222

Delivery vectors

• spear_phishing_attachments
• malicious_office_macros
• software_cracks

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run
• Scheduled Task Creation

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_QUASARRAT_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Quasarrat"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "quasarrat" ascii wide nocase
        $s2 = "quasar rat" ascii wide nocase
        $s3 = "quasar" ascii wide nocase
        $s4 = "backdoor.msil.quasar" ascii wide nocase
        $s5 = "win32/quasar" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Quasarrat (Rat) Execution & Triage
id: 44cf2879-504c-50db-b642-f3facbcacf5c
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Quasarrat 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/quasarrat
- 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.t1059_003
- attack.t1056_001
- attack.t1573_002
- attack.t1021_001
- attack.t1547_001
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_QUASARRAT_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Quasarrat 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 = "quasarrat" 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. Terminate suspicious .NET processes executing out of user temporary or AppData directories.
2. Inspect and remove unauthorized autostart registry entries under CurrentVersion\Run.
3. Sever active outbound TCP connections to unknown IP addresses on ports 4782 or 443.
4. Force domain password resets for all users whose workstations show evidence of Quasar execution.

What to Avoid

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

1. Do not treat Quasar as a legitimate administrative tool in enterprise environments; its presence indicates unauthorized access.
2. Avoid relying solely on default port monitoring; Quasar's C2 port is freely configurable by the operator.
3. Do not overlook infected developer machines where .NET tools might otherwise escape suspicion.

References & External Analysis

• CISA Advisory AA18-337A: Overview of Quasar RAT
• MITRE ATT&CK Software Profile: Quasar (S0262)
• GitHub: Quasar Development Repository
• CISA Advisory: AA18-337A
• Search "quasarrat" on VirusTotal (External Analysis)
• Search "quasarrat" on Any.Run (Sandbox Sandbox)
• Search "quasarrat" 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:

• Bandook
• Serenity_Rat
• Njrat
• Nuclear_Rat
• Protux
• Cybergate
• Nanocore
• Mokes

Machine-readable

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