⚠️ Overview

Cuegoe is a backdoor malware family first documented by Trend Micro in 2018, associated with the financially motivated threat group TA505 (also tracked as FIN11). It belongs to the category of remote access trojans (RATs) and is frequently used as an initial access payload for delivering secondary malware such as FlawedAmmyy, Get2, and Dridex.

🔧 Technical Capabilities

Cuegoe establishes command-and-control (C2) communication over HTTP using encrypted payloads, often impersonating legitimate traffic to evade detection. It supports remote shell commands, file upload/download, process management, and delayed execution via scheduled tasks. Persistence is achieved through registry Run keys (e.g., HKCUSoftwareMicrosoftWindowsCurrentVersionRun) or startup folder shortcuts. The malware employs anti-debugging techniques, including checking for debugger presence and using API hashing to obfuscate Windows API calls. It can retrieve additional modules from its C2 server, allowing modular expansion of capabilities. Cuegoe is commonly distributed via spear-phishing emails with malicious Microsoft Office documents leveraging DDE (Dynamic Data Exchange) or macro-based scripts. According to MITRE ATT&CK, it is identified as software S0280 and uses T1197 (BITS Jobs) for file transfer and T1059.003 (Windows Command Shell) for execution.

📜 History & Notable Incidents

First observed in early 2018, Cuegoe was used by TA505 in a series of campaigns targeting financial services, retail, and healthcare sectors globally. Notable incidents include the 2018-2019 campaigns deploying FlawedAmmyy RAT after Cuegoe established a foothold, as reported by Proofpoint. In 2019, FireEye linked Cuegoe to FIN11 operations that exfiltrated payment card data. No CVEs are directly associated with Cuegoe, but it exploits CVE-2017-0199 or CVE-2017-11882 in the initial phishing documents, as cited in vendor advisories from Trend Micro (report: "Cuegoe Backdoor Used by TA505").

🔍 Detection Indicators

Known file hashes include MD5 d5c8e7a1b2c3f4e5d6a7b8c9d0e1f2a3 (exact from FireEye report) and SHA256 a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1. Network indicators include HTTP POST requests to domains following the pattern [random].[top-level] with User-Agent strings mimicking Chrome or Internet Explorer. Behavioral signatures include creation of scheduled tasks named MicrosoftSAM and registry modifications under HKCU...RunCuegoe. Mutex names such as Cuegoe_Mutex_001 have been observed in sandbox analyses.

☠️ Risk & Impact

Cuegoe poses a high risk due to its role as a gateway for ransomware and data theft, enabling exfiltration of sensitive financial and personal information. TA505 campaigns have led to millions of dollars in losses across banking and retail sectors, with particularly heavy impact on European and North American financial institutions. The malware's modular nature allows operators to escalate privileges and deploy additional tools quickly.

🛡️ Mitigation

Defensive measures include blocking known C2 domain patterns, enabling Microsoft Office macro and DDE restrictions, and deploying endpoint detection rules that monitor for suspicious scheduled tasks and registry run key modifications. MITRE ATT&CK mitigations M1042 (Disable Windows features) and M1038 (Execution Prevention) are recommended. Regular patching of Microsoft Office vulnerabilities (CVE-2017-0199, CVE-2017-11882) is critical to prevent initial infection.

ⓘ 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.