GootLoader Evasion via Massive ZIP Concatenation
BLUF
GootLoader has evolved its delivery mechanism by using "massive" malformed ZIP archives containing up to 1,000 concatenated layers to bypass automated sandboxes and inspection tools.
Executive Cost Summary
This cost analysis was developed by the CyberDax team using expert judgment and assisted analytical tools to support clarity and consistency.
For organizations affected by GootLoader malware delivery using massive ZIP concatenation to evade automated inspection controls:
· Low-end total cost: $800K – $1.5M
· (single-user infection, rapid containment, no secondary payload execution)
· Typical expected range: $1.5M – $4.5M
· (multiple endpoints impacted, extended investigation, precautionary business disruption)
· Upper-bound realistic scenarios: $4.5M – $8.0M
· (loader persistence confirmed, compliance actions triggered, insurer scrutiny)
Key Cost Drivers
· Duration of uncertainty around secondary payload deployment
· Number of endpoints requiring forensic validation or rebuild
· Business unit exposure in regulated or client-facing functions
· Incident response labor intensity due to evasion techniques
· Post-incident insurance premium adjustments and deductibles
Targeted Sectors
· Legal
· Insurance
· Professional services
Countries
· Global
First reported
· January 15, 2026
Last updated reporting
· January 16, 2026
APT Names
· No APT group has been named at this time
Suspected Criminal Organizations
· Gootkit/GootLoader (Cybercriminal, possible IAB for APTs).
TTPs
Initial Access
· T1566 Phishing
o Historically distributed via spam campaigns.
· T1189 Drive-by Compromise
o Luring users to compromised websites through SEO poisoning.
· T1608.006 SEO Poisoning
o Manipulating search engine results to place malicious pages at the top of results.
Execution
· T1059.007 Command and Scripting Interpreter JavaScript
o Executing malicious scripts (often via wscript.exe or cscript.exe) to initiate the infection.
· T1059.001 Command and Scripting Interpreter PowerShell
o Used in later stages to collect system information and establish C2 communication.
Persistence
· T1053.005 Scheduled Task/Job Scheduled Task
o Creating tasks to ensure the malware runs consistently after restarts.
· T1547.001 Boot or Logon Autostart Execution Registry Run Keys / Startup Folder
o Adding entries to Windows Registry keys to maintain a foothold.
Defense Evasion
· T1027 Obfuscated Files or Information
o Using heavily obfuscated JScript and PowerShell code to bypass security tools.
· T1140 Deobfuscate/Decode Files or Information
o Decoding malicious payloads in memory to avoid detection.
· T1055 Process Injection
o Injecting code into legitimate processes to hide malicious activity.
Discovery
· T1082 System Information Discovery – Gathering host details, such as OS version and hardware configurations.
· T1018 Remote System Discovery – Identifying other systems on the network for potential lateral movement.
Command and Control
· T1071.001 Application Layer Protocol Web Protocols
o Using HTTP/S for communication with command and control servers.
· T1105 Ingress Tool Transfer
o Downloading additional malware or post-exploitation tools like Cobalt Strike or SystemBC.
Malware name
· GootLoader
Malware sample
sha256
cbb94dd87c3ce335c75e57621412eedce013fcc77ac92ec57f7e74ac70dde119
Malware Family
· GootLoader/Gootkit.
Verdict
· Malicious (Loader)
Objectives
· Persistence via .LNK files
o Staging for follow-on payloads like Cobalt Strike or Ransomware.
o Creates a .LNK in the Startup folder pointing to a second script in a random directory; spawns complex PowerShell process trees.
CVEs and CVSS Vectors
· Not applicable
o This was a misconfiguration issue resolved by AWS.
Nessus ID
· Not applicable
Is this on the KEV list?
· Not applicable
Suggested Detection/ potential hunts
As a reminder, these are indicator rules. They are likely to be noisy.
For best results consider creating a data model and reviewing the traffic as a report.
Suricata
Alert on multiple PK\x05\x06 (EOCD) signatures within one file transfer.
alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE GootLoader ZIP Concatenation Evasion Detected"; flow:established,to_client; file_data; content:"PK|03 04|"; distance:0; pcre:"/(PK\x05\x06.*){2,}/s"; classtype:bad-unknown; sid:2026001; rev:1;)
SentinelOne
Large ZIP Extraction by Explorer/Browsers
EventType = "File Create" AND
(FileExtension = "zip" OR FileExtension = "js") AND
FileSize > 50MB AND
(ProcessName = "explorer.exe" OR ProcessName = "chrome.exe" OR ProcessName = "msedge.exe")
GootLoader JScript Execution from Temp
sql
(ProcessName = "wscript.exe" OR ProcessName = "cscript.exe") AND
CmdLine RegExp ".*\\AppData\\Local\\Temp\\.*\.js" AND
ParentProcessName = "explorer.exe"
Splunk
Excessive ZIP File Creation (Sysmon Event ID 11)
index=windows sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=11
file_name="*.zip"
| stats count by host, TargetFilename, Image
| where count > 1 OR (TargetFilename LIKE "%agreement%" AND count > 0)
Detection: Large File Download via Web Logs
tag=web
url_path="*.zip"
| where bytes > 100000000
| stats count by src, dest, url, bytes
Logic: GootLoader lures often use names like agreement.zip or contract.zip. Identifying these files when they have anomalously large sizes (due to concatenation or padding) helps pinpoint evasion attempts.
Delivery
· SEO poisoning directing users to forums where they download "contract" or "legal" templates in ZIP format.
Email Samples
Web-based delivery
References
The Hacker News
· hxxps://thehackernews.com/2026/01/gootloader-malware-uses-5001000.html
SC Magazine
· hxxps://www.scmagazine.com/news/how-gootloader-uses-malformed-zip-archives-to-evade-detection
VirusTotal
· hxxps://www.virustotal.com/gui/file/cbb94dd87c3ce335c75e57621412eedce013fcc77ac92ec57f7e74ac70dde119/details
