As soon as used completely by the cybercriminals behind REVil ransomware and the Gootkit banking trojan, GootLoader and its main payload have advanced into an preliminary entry as a service platform—with Gootkit offering data stealing capabilities in addition to the potential to deploy post-exploitation instruments and ransomware.
GootLoader is understood for utilizing search engine marketing (Website positioning) poisoning for its preliminary entry. Victims are sometimes enticed into clicking on malicious adware or hyperlinks disguised as authentic advertising and marketing, or on this case a authentic Google search directing the consumer to a compromised web site internet hosting a malicious payload masquerading as the specified file. If the malware stays undetected on the sufferer’s machine, it makes approach for a second-stage payload often called GootKit, which is a extremely evasive data stealer and distant entry Trojan (RAT) used to determine a persistent foothold within the sufferer’s community surroundings. GootKit can be utilized to deploy ransomware or different instruments, together with Cobalt Strike, for follow-on exploitation.
Detection of a brand new GootLoader variant actively being utilized by adversaries earlier this 12 months led to a broad risk looking marketing campaign by Sophos X-Ops MDR for GootLoader situations throughout buyer environments. As is typical of Gootloader, the brand new variant was discovered to be utilizing Website positioning poisoning—using search engine marketing techniques to place malicious web sites managed by GootLoader’s operators excessive within the outcomes for particular search phrases—to ship the brand new, JavaScript-based Gootloader bundle. On this case, we discovered the GootLoader actors utilizing search outcomes for details about a selected cat and a selected geography getting used to ship the payload: “Are Bengal Cats authorized in Australia?”
Throughout the risk hunt marketing campaign, MDR found a .zip archive used to ship GootLoader’s first-stage payload whereas reviewing an impacted consumer’s browser historical past. This allowed MDR to establish the compromised web site that was internet hosting the malicious payload. This report highlights the MDR investigation course of and the technical particulars of the uncovered GootLoader marketing campaign.
Technical Evaluation and Identification
First-stage payload
On March 27, 2024, the MDR workforce carried out a proactive risk looking marketing campaign throughout a number of prospects estates, following lately reported identification of a brand new GootLoader variant being actively exploited within the wild.
Our investigation revealed the risk actor was utilizing Website positioning poisoning by means of an simply accessed on-line discussion board discovered by way of a easy Google search, initiated by the consumer for ‘Do you want a license to personal a Bengal cat in Australia’. The primary search consequence took us to this URL:
hxxps[://]ledabel[.]be/en/are-bengal-cats-legal-in-australia-understanding-the-laws-and-regulations/#:~:textual content=Eachpercent20statepercent20andpercent20territorypercent20in,topercent20keeppercent20thempercent20aspercent20pets.
Instantly after the consumer clicks the hyperlink, a suspicious .zip file was downloaded to C:Customers<Username>DownloadsAre_bengal_cats_legal_in_australia_33924.zip onto the sufferer’s machine, and the consumer’s browser was directed to the URL hxxps:[//]www[.]chanderbhushan[.]com/doc[.]php.
Second-stage payload
Upon overview of the working processes, we had been capable of decide {that a} small JavaScript file was dropping a big JavaScript file on the location C:Customers<Username>AppDataRoamingMicrosoft on the consumer’s machine. Throughout our testing, the big JavaScript file generated by the malicious web site and its title, downloaded to the consumer’s %temp% listing, had been totally different every time the preliminary JavaScript was executed. The file we noticed on this case was named Temp1_Are_bengal_cats_legal_in_australia_33924.zipare_bengal_cats_legal_in_australia_80872.js.
We moreover noticed the creation of a scheduled activity named “Enterprise Aviation” with the command line “wscript REHABI~1.JS” (as proven in Determine 3). This was suspected to be a persistence methodology during which the risk actor was using WScript.exe to execute the second-stage payload of GootKit.
We additionally famous the utilization of the command C:WindowsSystem32cscript.exe REHABI~1.JS spawning PowerShell.exe, as proven in Determine 4. The cscript.exe command line device is particular to Home windows Server. The instructions handed to PowerShell weren’t captured on this case.
Nevertheless, analyzing the URL historical past, we noticed PowerShell.exe reaching out to the next domains, as proven in Determine 5. Third-stage payload
Within the case the MDR workforce examined, our workforce didn’t observe the third stage being profitable in reaching a full deployment of GootKit, stopping the obtain of any extra malicious tooling. This stage usually is the place the deployment of extra instruments similar to Cobalt Strike happens, or when ransomware is added to the sufferer’s machine.
Malware Triage
Static Evaluation
MDR carried out a static evaluation of the of the .zip pattern obtained from the malicious URL hxxps[://]ledabel[.]be/en/are-bengal-cats-legal-in-australia-understanding-the-laws-and-regulations/#:~:textual content=Inpercent20mostpercent20casespercent2Cpercent20youpercent20do,apercent20Bengalpercent20catpercent20inpercent20Australia. Throughout the zip file was a JavaScript named “are bengal cats authorized in australia 72495.js”.
As we famous above, the JavaScript’s title is modified every time the file is downloaded with a special concluding numerical sequence. This was additionally noticed when extracting the small JavaScript from the zip file, as proven in Determine 6. For instance, customers could observe a filename with are bengal cats authorized in australia 75876.zip as an alternative, when making an attempt to acquire a pattern from the malicious URL.
A string evaluation of the dropped file was not helpful in figuring out its intent, because the JavaScript was closely obfuscated—as is frequent in Gootloader samples. The script additionally included boilerplate licensing feedback to make it seem like a authentic JavaScript, as proven in Determine 7.
Nevertheless, Strings evaluation of the secondary bigger JavaScript that was downloaded into C:Customers<Username>AppDataRoamingNotepad++Small Unit Ways.js revealed a closely obfuscated script, as proven in Determine 8.
MDR used a Python script created by Mandiant for auto-decoding of GootLoader JavaScript to statically analyze the initially downloaded Are_bengal_cats_legal_in_australia_72495.js. As proven in Determine 9, the file was recognized as Gootloader variant 3.0 by means of the obfuscation methodology, the place the primary file created was named Huthwaite SPIN promoting.dat adopted by Small Models Ways.js and Scheduled Job named Vacation spot Branding. The decoder additionally recognized varied malicious domains inside the obfuscated strings.
Dynamic evaluation
Varied dynamic evaluation instruments had been utilized to look at the conduct of the malicious JavaScript. Upon execution, WScript.exe was noticed creating the primary file situated inside C:Customers<Username>AppDataRoamingNotepad++ , as proven in Determine 10. Regardless of being noticed by way of Home windows Sysinternals Course of Monitor with a CreateFile occasion, this was not written to disk and no deletion occasion was seen.
Shortly after Wscript.exe executed Are_bengal_cats_legal_in_australia_72495.js, Course of Hacker confirmed CScript.exe and Powershell.exe being created with a conhost.exe spawned, as proven in Determine 11. MDR noticed that Wscript.exe would terminate, adopted by Cscript.exe that may additionally terminate shortly after, after which Powershell.exe was created.
Persistence was obtained by way of CScript.exe executing the file SMALLU~1.js by way of a scheduled activity named Vacation spot Branding (with command line wscript SMALLU ~1.js , as proven in Determine 12). Throughout the lab evaluation, the secondary JavaScript might be dropped inside any folders situated inside C:Customers<Username>AppDataRoaming<at any present folder>.
MDR performed community and C2 examinations utilizing Wireshark and FakeNet to carry out a community seize in the course of the execution of Are_bengal_cats_legal_in_australia_72495.js. FakeNet confirmed varied domains being reached out to with GET /xmlrpc.php HTTP/1.1 requests by way of Powershell.exe. The requests contained Base64-encoded cookies which, when decoded, confirmed enumeration data concerning system directories and host data such because the folder path of C:Customers<Username>AppDataRoaming , as proven in Determine 13. As proven under, the method would learn USERNAME and USER DOMAIN data and ship the info to the URIs.
Examination of the PCAP seize lists varied domains that had been additionally recognized throughout static evaluation, as proven in Determine 14. These domains and IOCs have been categorized by Sophos Labs as malware/callhome ; the preliminary and secondary JavaScript information are categorized as JS/Drop-DIJ and JS/Gootkit-AW respectively.
MITRE mapping
The next chart maps the noticed techniques to the MITRE ATT&CK® framework.
Tactic
Method
Sub-Method
ID
Reconnaissance
Useful resource Improvement
Stage Capabilities
Add Malware
Website positioning Poisoning
T1608.001
T1608.006
Preliminary Entry
Drive-by Compromise
T1189
Execution
Command and Scripting Interpreter
JavaScript
T1059.007
Persistence
Scheduled Job/Job
Scheduled Job
T1053.005
Privilege Escalation
Protection Evasion
Obfuscated Recordsdata or Info
Embedded Payloads
T1027.009
Credential Entry
Discovery
System Info Discovery
T1082
Lateral Motion
Assortment
Command and Management
Exfiltration
Exfiltration Over Net Service
T1567
Influence
Conclusion
GootLoader is considered one of plenty of persevering with malware-delivery-as-a-service operations that closely leverage search outcomes as a way to achieve victims. The usage of search engine marketing, and abuse of search engine promoting to lure targets to obtain malware loaders and dropper, aren’t new—GootLoader has been doing this since at the least 2020, and we’ve noticed Raccoon Stealer and different malware-as-a-service operations doing the identical for simply as lengthy. However we’ve seen continued progress on this method to preliminary compromise, with a number of large campaigns utilizing this method over the previous 12 months.
Sophos endpoint safety blocks GootLoader by means of plenty of behavioral and malware-specific detections. However customers ought to nonetheless look out for search outcomes and search ads that appear too good to be true on domains which can be off the overwhelmed path—whether or not they’re seeking to get a Bengal Cat or not.
Indicators of Compromise
An inventory of IOCs is accessible as a CSV file within the Sophos GitHub repository right here.
