For the past month or so, I hadn’t had any luck finding active malspam campaigns pushing Dridex malware. That changed starting this week, and I’ve since found several examples. Today’s diary reviews an infection from Wednesday September 9th, 2020.
The Word documents
While searching VirusTotal, I found three documents with the same template that generated the same type of traffic (read: SHA256 hash – name):
- fee5bb973112d58445d9e267e0ceea137d9cc1fb8a7140cf9a67472c9499a30f – Info-3948683568.doc
- 9b747e89874c0b080cf78ed61a1ccbd9c86045dc61b433116461e3e81eee1348 – Inform-34674869.doc’
- 27379612c139d3c4a0c6614ea51d49f2495213c867574354d7851a86fdec2428 – Rep-Sept2020.doc
My lab environment revealed these documents are designed to infect a vulnerable Windows host with Dridex.
Enabling macros caused Powershell to retrieve a DLL file from one of the following URLs over encrypted HTTPS traffic:
hxxps://teworhfoundation[.]com/4jvmow.zip hxxps://teworhfoundation[.]com/zd0pcc.rar hxxps://thecandidtales[.]com/doakai.zip hxxps://safaktasarim[.]com/7zcsfo.txt hxxps://thecandidtales[.]com/wuom4a.rar
After the DLL was saved under the victim’s profile, it was run using rundll32.exe. The DLL is an installer for Dridex, and it was run using the following command:
"C:Windowssystem32rundll32.exe" C:Users[username]Mqfzqp8Opzvzn2Qzpic6r.dll 0
Dridex infection traffic
Dridex post-infection traffic is all HTTPS. In this case, we saw HTTPS traffic over the following IP addresses and ports:
67.213.75[.]205 port 443 54.39.34[.]26 port 453
Most of the Dridex post-infection traffic I’ve seen uses IP addresses without domain names, and issuer data for the SSL/TLS certificates is somewhat unusual. Certificate issuer data for the Dridex post-infection traffic:
CERTIFICATE ISSUER DATA FOR HTTPS TRAFFIC TO 67.213.75[.]205 OVER TCP PORT 443: id-at-countryName=HR id-at-localityName=Zagreb id-at-organizationName=Wageng Unltd. id-at-organizationalUnitName=obendmma id-at-commonName=Livedthtsthw.flights CERTIFICATE ISSUER DATA FOR HTTPS TRAFFIC TO 54.39.34[.]26 OVER TCP PORT 453: id-at-countryName=DE id-at-stateOrProvinceName=Sheso thanthefo id-at-localityName=Berlin id-at-organizationName=Thedelor Tbrra SICAV id-at-organizationalUnitName=5Coiesily Begtherdr istwarscon id-at-commonName=Bath7epran.toshiba
Dridex persistent on an infected Windows host
Dridex is made persistent on an infected Windows host using 3 methods simultaneously:
- Windows registry update
- Scheduled task
- Windows startup menu shortcut
Dridex uses copies of legitimate Windows system files (EXEs) to load and run malware. Dridex DLL files are named as DLLs that would normally be run by these copied system EXEs.
For this infection, all of the persistent Dridex DLL files were 64-bit DLL files.
WINDOWS REGISTRY UPDATE: - Registry Key: HKCUSOFTWAREMicrosoftWindowsCurrentVersionRun - Value name: Vwqmkqmr - Value type: REG_SZ - Value data: C:Users[username]AppDataRoamingThunderbirdProfiles1ovarfyl.default-release ImapMail.outlook.comUw0NWHoOiDWWIN.EXE NOTE: DWWIN.EXE loads and runs a Dridex DLL file named VERSION.dll in the same directory.
SCHEDULED TASK: - Task name: Qgdopf - Action: Start a program - Details: C:Users[username]AppDataRoamingMicrosoftWindowsStart MenuProgramsAccessories 0pFtxbOGXwrDmNotificationBroker.exe NOTE: DmNotificationBroker.exe loads and runs a Dridex DLL file named DUI70.dll in the same directory.
WINDOWS STARTUP MENU SHORTCUT: Shortcut: C:Users[username]AppDataRoamingMicrosoftWindowsStart MenuSomdjvzvjfch.lnk Target: C:Users[username]AppDataRoamingMozillaExtensionsr0Fmsinfo32.exe NOTE: msinfo32.exe loads and runs a Dridex DLL file named MFC42u.dll in the same directory.
Indicators of Compromise (IOCs)
Three examples of Microsoft Word documents with macros for Dridex:
- File size: 136,262 bytes
- File name: Info-3948683568.doc
- File size: 136,182 bytes
- File name: Inform-34674869.doc
- File size: 135,053 bytes
- File name: Rep-Sept2020.doc
Installer DLL for Dridex called by Word macro:
- File size: 331,776 bytes
- File location: hxxps://thecandidtales[.]com/doakai.zip
- File location: C:Users[username]MqFZqp8OpZVzn2Qzpic6r.dll
- Run method: rundll32.exe [file name] 0
Dridex 64-bit DLL files persistent on the infected Windows host:
- File size: 1,580,032 bytes
- File location: C:Users[username]AppDataRoamingMicrosoftWindowsStart MenuProgramsAccessoriespFtxbOGXwrDUI70.dll
- Run method: Loaded and run by legitimate system file DmNotificationBroker.exe in the same directory
- Note: Made persistent through scheduled task
- File size: 1,325,056 bytes
- File location: C:Users[username]AppDataRoamingMozillaExtensionsr0FMFC42u.dll
- Run method: Loaded and run by legitimate system file msinfo32.exe in the same directory
- Note: Made persistent through start menu shortcut
- File size: 1,297,920 bytes
- File location: C:Users[username]AppDataRoamingThunderbirdProfiles1ovarfyl.default-releaseImapMail.outlook.comUw0NWHoOiVERSION.dll
- Run method: Loaded and run by legitimate system file DWWIN.EXE in the same directory
- Note: Made persistent through Windows registry update
URLs from Word macro to retrieve Dridex DLL installer:
Certificate data for Dridex HTTPS traffic to 67.213.75[.]205 port 443:
- id-at-organizationName=Wageng Unltd.
Certificate data for Dridex HTTPS traffic to 54.39.34[.]26 port 453:
- id-at-stateOrProvinceName=Sheso thanthefo
- id-at-organizationName=Thedelor Tbrra SICAV
- id-at-organizationalUnitName=5Coiesily Begtherdr istwarscon
After a period of inactivity, malspam pushing Dridex malware is back, so this blog post reviewed traffic and malware from an infected Windows host. While not much has changed, it’s always good to have a refresher.
As usual, up-to-date Windows hosts with the latest security patches and users who follow best security practices are not likely to get infected with this malware. However, I’ve seen so much come through in the past two or three days that even a small percentage of success will likely be profitable for the criminals behind it.
brad [at] malware-traffic-analysis.net
(c) SANS Internet Storm Center. https://isc.sans.edu Creative Commons Attribution-Noncommercial 3.0 United States License.