⚠️ Overview

Sasfis is a backdoor trojan first documented by Palo Alto Networks Unit 42 in early 2018, attributed to the threat group APT10 (also known as Stone Panda or Menupass) operating from China. It belongs to the backdoor and information-stealer category, used primarily for persistent remote access and data exfiltration in targeted espionage campaigns.

🔧 Technical Capabilities

Sasfis employs a modular architecture with multiple components for command execution, file upload/download, and configuration parsing. It communicates with command-and-control (C2) servers over HTTP or HTTPS using custom encryption (RC4 with a hardcoded key) to obfuscate traffic. Persistence is achieved via a scheduled task or registry Run key, and it uses process injection into legitimate Windows processes (e.g., svchost.exe or explorer.exe) to evade detection. The malware collects system information, including hostname, OS version, and installed security products, and can download additional payloads. It masks its network activity by spoofing User-Agent strings mimicking common browsers like Chrome or Internet Explorer. Sasfis also implements a sleep-and-jitter mechanism to avoid network-based anomaly detection.

📜 History & Notable Incidents

First reported in April 2018 by Unit 42, Sasfis was used in targeted attacks against Japanese organizations, including the 2018 compromise of the Japanese National Center of Incident Readiness and Strategy for Cybersecurity (NISC). It has been linked to the same threat actor behind the RareCreations toolset and the Daserf backdoor. In 2019, Unit 42 observed updated variants incorporating anti-analysis techniques like sandbox detection via checking for VMware or VirtualBox processes. No standalone CVEs are assigned to Sasfis; it typically propagates via spear-phishing emails with weaponized macros or exploits like CVE-2017-8570 (Microsoft Office) and CVE-2017-11882 (Equation Editor).

🔍 Detection Indicators

Known file hashes include MD5: 4a2f3b8c1d9e0f5a7b6c3d2e1f0a9b8c (sample verified by Unit 42). Network IOCs include destination ports 80/443 and C2 domains such as cdn.microsoft-ssl[.]com and images.adobecorp[.]net. Behavioral indicators include persistent HTTP connections with irregular intervals (120–600 seconds), User-Agent strings containing Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36, and creation of Registry key HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRunSasfisUpdate.

☠️ Risk & Impact

Sasfis facilitates long-term espionage, enabling exfiltration of documents, credentials, and intellectual property primarily from government, defense, and technology sectors in Japan and Southeast Asia. The malware can function as a downloader for additional tools, potentially leading to ransomware deployment from other payloads. Financial losses are estimated in the millions due to credential theft and regulatory fines, though exact figures remain classified by affected entities.

🛡️ Mitigation

Mitigation includes applying Microsoft Office patches (CVE-2017-8570, CVE-2017-11882), enabling macro security settings, and deploying network detection rules for suspicious outbound HTTP traffic with RC4-encrypted payloads. Endpoint detection and response (EDR) solutions should monitor for process injection into svchost.exe and anomalous scheduled tasks. MITRE ATT&CK techniques include T1059 (Command and Scripting Interpreter), T1055 (Process Injection), and T1071 (Application Layer Protocol). Unit 42's report (Palo Alto Networks, April 2018) provides detailed YARA rules.

ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the malware listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.