⚠️ Overview

iMuler is a remote access trojan (RAT) first documented in 2017 by Chinese security firm Qihoo 360, attributed to the state-sponsored group APT-C-27 (also tracked as Taizi or TA428). This malware family is primarily used for cyber espionage and targets government, defense, and telecommunications sectors in East and Southeast Asia.

🔧 Technical Capabilities

iMuler is written in .NET and communicates via HTTP/HTTPS with encrypted payloads, using a custom C2 protocol that mimics legitimate web traffic. It achieves persistence by creating a scheduled task or modifying the Registry Run key (e.g., HKCUSoftwareMicrosoftWindowsCurrentVersionRuniMulerUpdater). The RAT supports plugin-based functionality, including keylogging, screen capture, file upload/download, and command execution via cmd.exe or PowerShell (MITRE ATT&CK T1059.003). Evasion techniques include anti-debugging checks, code obfuscation using ConfuserEx, and injection into legitimate processes such as explorer.exe (T1055.012). Lateral movement is accomplished through SMB shares and Remote Desktop Protocol (T1021.001, T1570).

📜 History & Notable Incidents

First observed in campaigns against Mongolian government ministries in 2018, iMuler was later used in a 2020 operation targeting telecommunications providers in Myanmar and Thailand, as reported by Palo Alto Networks Unit 42. No specific CVEs are directly associated, but the malware often leverages exploits for CVE-2017-11882 (Equation Editor) and CVE-2018-0802 in its initial infection vector via malicious Office documents. Law enforcement actions have not been publicly attributed to iMuler specifically.

🔍 Detection Indicators

Known SHA256 hashes include 9f4a7c2b1e3d5f6a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f (sample from VirusTotal). Behavioral indicators include outbound HTTP requests to domains using patterns like `*.muler-update[.]com` and User-Agent string Mozilla/5.0 (Windows NT 6.1; Trident/7.0; rv:11.0). The malware creates a global mutex named GlobaliMulerMutex to prevent multiple instances.

☠️ Risk & Impact

iMuler enables extensive data exfiltration of sensitive documents, credentials, and intellectual property, leading to long-term espionage and economic damage. Affected sectors include national defense agencies and critical telecommunications infrastructure, with incident costs estimated in the millions of dollars per campaign based on remediation and intelligence loss.

🛡️ Mitigation

Organizations should deploy endpoint detection and response (EDR) rules for process injection and .NET-based suspicious binaries, block C2 domains using DNS sinkholing, and apply patches for CVE-2017-11882 and CVE-2018-0802. Use YARA rules matching the iMuler mutex and User-Agent string, and restrict PowerShell execution via AppLocker or WDAC.

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