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Doctor Web: M.E.Doc backdoor lets cybercriminals access computers

July 4, 2017

Doctor Web security researchers examined the update module M.E.Doc and discovered that it is involved in the distribution of at least one other malicious program. You may recall that independent researchers named specifically this M.E.Doc update module as the source of the recent outbreak of the encryption worm Trojan.Encoder.12544, also known as NePetya, Petya.A, ExPetya and WannaCry-2. M.E.Doc is tax accounting software that is popular in Ukraine.

The reports state that Trojan.Encoder.12544 was first distributed via M.E.Doc, the popular application developed by the Ukrainian company Intellect Service. Doctor Web security researchers found that one of the M.E.Doc update system’s modules, ZvitPublishedObjects.Server.MeCom, contained a record corresponding to a specific Windows system registry key: HKCU\SOFTWARE\WC.

screenshot BackDoor.Medoc #drweb

Doctor Web specialists noted this registry key because Trojan.Encoder.12703 uses the same path for its operation. An analysis of the Dr.Web Anti-virus log obtained from one of our customer’s computers showed that Trojan.Encoder.12703 was launched on the infected machine by the application ProgramData\Medoc\Medoc\ezvit.exe, which is a component of M.E.Doc:

screenshot BackDoor.Medoc #drweb

id: 425036, timestamp: 15:41:42.606, type: PsCreate (16), flags: 1 (wait: 1), cid: 1184/5796:\Device\HarddiskVolume3\ProgramData\Medoc\Medoc\ezvit.exe

source context: start addr: 0x7fef06cbeb4, image: 0x7fef05e0000:\Device\HarddiskVolume3\Windows\Microsoft.NET\Framework64\v2.0.50727\mscorwks.dll

created process: \Device\HarddiskVolume3\ProgramData\Medoc\Medoc\ezvit.exe:1184 --> \Device\HarddiskVolume3\Windows\System32\cmd.exe:6328

bitness: 64, ilevel: high, sesion id: 1, type: 0, reason: 1, new: 1, dbg: 0, wsl: 0

curdir: C:\Users\user\Desktop\, cmd: "cmd.exe" /c %temp%\wc.exe -ed BgIAAACkAABSU0ExAAgAAAEAAQCr+LiQCtQgJttD2PcKVqWiavOlEAwD/cOOzvRhZi8mvPJFSgIcsEwH8Tm4UlpOeS18o EJeJ18jAcSujh5hH1YJwAcIBnGg7tVkw9P2CfiiEj68mS1XKpy0v0lgIkPDw7eah2xX2LMLk87P75rE6 UGTrbd7TFQRKcNkC2ltgpnOmKIRMmQjdB0whF2g9o+Tfg/3Y2IICNYDnJl7U4IdVwTMpDFVE+q1l+Ad9 2ldDiHvBoiz1an9FQJMRSVfaVOXJvImGddTMZUkMo535xFGEgkjSDKZGH44phsDClwbOuA/gVJVktXvD X0ZmyXvpdH2fliUn23hQ44tKSOgFAnqNAra

status: signed_microsoft, script_vm, spc / signed_microsoft / clean

id: 425036 ==> allowed [2], time: 0.285438 ms

2017-Jun-27 15:41:42.626500 [7608] [INF] [4480] [arkdll]

id: 425037, timestamp: 15:41:42.626, type: PsCreate (16), flags: 1 (wait: 1), cid: 692/2996:\Device\HarddiskVolume3\Windows\System32\csrss.exe

source context: start addr: 0x7fefcfc4c7c, image: 0x7fefcfc0000:\Device\HarddiskVolume3\Windows\System32\csrsrv.dll

created process: \Device\HarddiskVolume3\Windows\System32\csrss.exe:692 --> \Device\HarddiskVolume3\Windows\System32\conhost.exe:7144

bitness: 64, ilevel: high, sesion id: 1, type: 0, reason: 0, new: 0, dbg: 0, wsl: 0

curdir: C:\windows\system32\, cmd: \??\C:\windows\system32\conhost.exe "1955116396976855329-15661177171169773728-1552245407-149017856018122784351593218185"

status: signed_microsoft, spc / signed_microsoft / clean

id: 425037 ==> allowed [2], time: 0.270931 ms

2017-Jun-27 15:41:43.854500 [7608] [INF] [4480] [arkdll]

id: 425045, timestamp: 15:41:43.782, type: PsCreate (16), flags: 1 (wait: 1), cid: 1340/1612:\Device\HarddiskVolume3\Windows\System32\cmd.exe

source context: start addr: 0x4a1f90b4, image: 0x4a1f0000:\Device\HarddiskVolume3\Windows\System32\cmd.exe

created process: \Device\HarddiskVolume3\Windows\System32\cmd.exe:1340 --> \Device\HarddiskVolume3\Users\user\AppData\Local\Temp\wc.exe:3648

bitness: 64, ilevel: high, sesion id: 1, type: 0, reason: 1, new: 1, dbg: 0, wsl: 0

curdir: C:\Users\user\Desktop\, cmd: C:\Users\user\AppData\Local\Temp\wc.exe -ed BgIAAACkAABSU0ExAAgAAAEAAQCr+LiQCtQgJttD2PcKVqWiavOlEAwD/cOOzvRhZi8mvPJFSgIcsEwH8Tm4UlpOeS18oE JeJ18jAcSujh5hH1YJwAcIBnGg7tVkw9P2CfiiEj68mS1XKpy0v0lgIkPDw7eah2xX2LMLk87P75rE6U GTrbd7TFQRKcNkC2ltgpnOmKIRMmQjdB0whF2g9o+Tfg/3Y2IICNYDnJl7U4IdVwTMpDFVE+q1l+Ad92 ldDiHvBoiz1an9FQJMRSVfaVOXJvImGddTMZUkMo535xFGEgkjSDKZGH44phsDClwbOuA/gVJVktXvDX 0ZmyXvpdH2fliUn23hQ44tKSOgFAnqNAra

fileinfo: size: 3880448, easize: 0, attr: 0x2020, buildtime: 01.01.2016 02:25:26.000, ctime: 27.06.2017 15:41:42.196, atime: 27.06.2017 15:41:42.196, mtime: 27.06.2017 15:41:42.196, descr: wc, ver: 1.0.0.0, company: , oname: wc.exe

hash: 7716a209006baa90227046e998b004468af2b1d6 status: unsigned, pe32, new_pe / unsigned / unknown

id: 425045 ==> undefined [1], time: 54.639770 ms

The file ZvitPublishedObjects.dll, which was requested from the infected machine, had the same hash as a sample examined in the Doctor Web virus laboratory. Thus, our security researchers concluded that the M.E.Doc update module, which is implemented as the dynamic library ZvitPublishedObjects.dll, contains a backdoor. Further research showed that this backdoor can execute the following functions in the infected system:

  • Collect data for accessing mail servers;
  • Execute arbitrary commands in the infected system;
  • Load arbitrary files to the infected computer;
  • Load, save and start any executable files;
  • Upload arbitrary files to a remote server.

The following code fragment of the M.E.Doc update module looks rather unique—it allows the payload to be launched using the tool rundll32.exe with the parameter #1:

screenshot BackDoor.Medoc #drweb

This is exactly how the encryption Trojan, known as NePetya, Petya.A, ExPetya and WannaCry-2 (Trojan.Encoder.12544), was launched on the computers of victims.

Reuters published an interview with the developers of M.E.Doc who stated that their application contains no malicious functions. Because of that, and also taking into account the results of a static code analysis, Doctor Web security researchers concluded that some unidentified cybercriminals infected one of M.E.Doc’s components with the malicious program. This component was added to the Dr.Web virus databases under the name BackDoor.Medoc.

More about this Trojan

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