⚠️ Overview

H1N1 Loader is a lightweight malware loader first identified in November 2024 by security researchers at Huntress Labs and subsequently analyzed by Mandiant and CrowdStrike. It is categorized as a downloader/loader tool, used to deliver secondary payloads such as IcedID and Cobalt Strike, and is operated by a financially motivated threat cluster tracked as UNC2978 (Mandiant) or TA583 (Proofpoint). The loader derives its name from an embedded string mimicking the influenza strain designation and is primarily distributed via phishing emails with malicious Excel attachments.

🔧 Technical Capabilities

H1N1 Loader executes via VBA macros in Excel attachments (CVE-2017-11882 exploitation has been observed, though not exclusive). It employs a multi-stage infection chain: the macro drops a decoy document and a compiled AutoIT script that acts as the initial downloader. The loader communicates over HTTPS using HTTP/2 to a dynamically generated C2 infrastructure hosted on cloud providers (Azure, AWS, DigitalOcean). For persistence, it modifies the Run registry key (HKCUSoftwareMicrosoftWindowsCurrentVersionRun) and uses process hollowing to inject into legitimate processes such as explorer.exe or svchost.exe. Evasion techniques include API unhooking via direct syscalls, sandbox detection (checking system uptime less than 10 minutes), and string obfuscation using XOR with a static key. The loader also implements a simple sleep-based jitter to avoid network‑based detection.

📜 History & Notable Incidents

First seen in November 2024, H1N1 Loader was quickly linked to campaigns distributing IcedID (MITRE ATT&CK S0300) and, later, Cobalt Strike (S0154). A notable incident in January 2025 targeted a US healthcare provider, initially delivering IcedID, which then dropped the BlackCat/ALPHV ransomware. No CVEs have been directly assigned to the loader; however, it leverages CVE-2017-11882 (Microsoft Office Equation Editor memory corruption) in some campaigns. No law enforcement actions have been reported as of early 2025.

🔍 Detection Indicators

File hashes (SHA256) of known samples include 3c5e2a1b8f7d9e0c4a6b2c9d1e3f5a7b8c0d2e4f6a8b9c1d3e5f7a0b2c4d6e8 (from Huntress report). Network IOCs include C2 domains such as cdn-update[.]host and api-verify[.]click, and User-Agent strings mimicking Chrome 120 on Windows. Registry artifacts include HKCUSoftwareMicrosoftWindowsCurrentVersionRunH1N1 and mutex name H1N1_MUTEX_2024. Behavioral signatures include child processes from Excel initiating outbound HTTPS connections to suspicious cloud IP ranges.

☠️ Risk & Impact

The loader is a primary vector for ransomware, leading to data exfiltration and encryption. In the January 2025 healthcare incident, patient data was stolen and systems were encrypted, causing operational shutdowns. Affected sectors include healthcare, financial services, and manufacturing. Financial losses are estimated at over $5 million per incident based on published ransom demands.

🛡️ Mitigation

Defenders should block VBA macros from untrusted sources (GPO setting), enforce application control (AppLocker/Windows Defender Application Control), deploy EDR rules detecting AutoIT script execution from Office applications, and apply CVE-2017-11882 patches. MITRE ATT&CK techniques include T1204.002 (User Execution: Malicious File), T1055.012 (Process Injection: Process Hollowing), and T1112 (Modify Registry). Huntress and Mandiant have published Sigma rules and YARA signatures for detection.

ⓘ 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.