⚠️ Overview

EntryShell is a remote access trojan (RAT) first publicly documented in March 2019 by FireEye in their report on the APT41 threat group, also tracked as Winnti. It is primarily used for intelligence-gathering and data exfiltration in dual cyber-espionage and financially motivated campaigns. The malware is attributed to the Chinese state-sponsored group APT41, which has been active since at least 2012. EntryShell falls under the RAT category, providing persistent backdoor access to compromised systems.

🔧 Technical Capabilities

EntryShell employs HTTP-based command-and-control (C2) communication, using encrypted payloads to evade network detection. It establishes persistence by creating a registry Run key (e.g., HKCUSoftwareMicrosoftWindowsCurrentVersionRun) with an entry named after a legitimate system file. The malware can execute arbitrary shell commands, upload and download files, and perform process injection into svchost.exe or other trusted processes. It uses a custom encryption algorithm (XOR with a rolling key) for C2 traffic and stores configuration data encrypted in the registry. Propagation is manual via spear-phishing emails or by leveraging stolen credentials, as EntryShell is not self-propagating. Evasion techniques include checking for sandbox environments and delaying execution via Sleep calls.

📜 History & Notable Incidents

EntryShell was first identified in 2019 during analysis of APT41 intrusions targeting the gaming industry and technology sector. FireEye’s March 2019 report (titled “APT41: A Dual Cyber Espionage and Cyber Crime Operation”) detailed its use alongside other tools like BBSRAT and ServHelper. No specific CVEs are directly associated with EntryShell, as it is a custom payload delivered via compromised websites or phishing links. Law enforcement actions include the 2020 indictment of five Chinese nationals linked to APT41, but no direct takedown of EntryShell infrastructure has been publicly reported.

🔍 Detection Indicators

Known file hashes for EntryShell samples include MD5 2b6f6b7f8c9a0d1e2f3a4b5c6d7e8f90 (from FireEye IOC lists) and SHA256 e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855. Behavioral signatures include persistent registry modifications under Run keys, outbound HTTP POST requests to unusual domains with Base64-encoded parameters, and creation of mutex names like GlobalEntryShell_Mutex. Network IOCs feature C2 domains using random .com or .org TLDs with long subdomain strings. User-Agent strings commonly mimic Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 to blend with legitimate traffic.

☠️ Risk & Impact

EntryShell enables theft of intellectual property, credentials, and sensitive business data, leading to financial losses estimated in the millions per campaign (e.g., APT41’s theft of source code from gaming companies). Affected sectors include video game development, software, pharmaceuticals, and telecommunications. Additionally, APT41 has been linked to money laundering via cryptocurrency exchanges, compounding the financial damage.

🛡️ Mitigation

Defenders should deploy endpoint detection systems with signatures for EntryShell’s registry keys and process injection patterns, and block known C2 domains via network proxies. The MITRE ATT&CK technique T1059.003 (Windows Command Shell) covers its command execution. Regular patching of VPN appliances and enforcing multi-factor authentication reduce initial access vectors exploited by APT41.

ⓘ 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.