FireEye Labs recently observed an attack against the government sector in Central Asia. The attack involved the new HAWKBALL backdoor being delivered via well-known Microsoft Office vulnerabilities CVE-2017-11882 and CVE-2018-0802.

HAWKBALL is a backdoor that attackers can use to collect information from the victim, as well as to deliver payloads. HAWKBALL is capable of surveying the host, creating a named pipe to execute native Windows commands, terminating processes, creating, deleting and uploading files, searching for files, and enumerating drives.

Figure 1 shows the decoy used in the attack.

Figure 1: Decoy used in attack

The decoy file, doc.rtf (MD5: AC0EAC22CE12EAC9EE15CA03646ED70C), contains an OLE object that uses Equation Editor to drop the embedded shellcode in %TEMP% with the name 8.t. This shellcode is decrypted in memory through EQENDT32.EXE. Figure 2 shows the decryption mechanism used in EQENDT32.EXE.

Figure 2: Shellcode decryption routine

The decrypted shellcode is dropped as a Microsoft Word plugin WLL (MD5: D90E45FBF11B5BBDCA945B24D155A4B2) into C:\Users\ADMINI~1\AppData\Roaming\Microsoft\Word\STARTUP (Figure 3).

Figure 3: Payload dropped as Word plugin

Technical Details

DllMain of the dropped payload determines if the string WORD.EXE is present in the sample’s command line. If the string is not present, the malware exits. If the string is present, the malware executes the command RunDll32.exe < C:\Users\ADMINI~1\AppData\Roaming\Microsoft\Word\STARTUP\hh14980443.wll, DllEntry> using the WinExec() function.

DllEntry is the payload’s only export function. The malware creates a log file in %TEMP% with the name c3E57B.tmp. The malware writes the current local time plus two hardcoded values every time in the following format:

<Month int>/<Date int> <Hours>:<Minutes>:<Seconds>\t<Hardcoded Digit>\t<Hardcoded Digit>\n

Example:

05/22 07:29:17 4          0

This log file is written to every 15 seconds. The last two digits are hard coded and passed as parameters to the function (Figure 4).

Figure 4: String format for log file

The encrypted file contains a config file of 0x78 bytes. The data is decrypted with an 0xD9 XOR operation. The decrypted data contains command and control (C2) information as well as a mutex string used during malware initialization. Figure 5 shows the decryption routine and decrypted config file.

Figure 5: Config decryption routine

The IP address from the config file is written to %TEMP%/3E57B.tmp with the current local time. For example:

05/22 07:49:48 149.28.182.78.

Mutex Creation

The malware creates a mutex to prevent multiple instances of execution. Before naming the mutex, the malware determines whether it is running as a system profile (Figure 6). To verify that the malware resolves the environment variable for %APPDATA%, it checks for the string config/systemprofile.

Figure 6: Verify whether malware is running as a system profile

If the malware is running as a system profile, the string d0c from the decrypted config file is used to create the mutex. Otherwise, the string _cu is appended to d0c and the mutex is named d0c_cu (Figure 7).

Figure 7: Mutex creation

After the mutex is created, the malware writes another entry in the logfile in %TEMP% with the values 32 and 0.

Network Communication

HAWKBALL is a backdoor that communicates to a single hard-coded C2 server using HTTP. The C2 server is obtained from the decrypted config file, as shown in Figure 5. The network request is formed with hard-coded values such as User-Agent. The malware also sets the other fields of request headers such as:

• Content-Length: <content_length>
• Cache-Control: no-cache
• Connection: close

The malware sends an HTTP GET request to its C2 IP address using HTTP over port 443. Figure 8 shows the GET request sent over the network.

Figure 8: Network request

The network request is formed with four parameters in the format shown in Figure 9.

Format = "?t=%d&&s=%d&&p=%s&&k=%d"

Figure 9: GET request parameters formation

Table 1 shows the GET request parameters.

Table 1: GET request parameters

If the returned response is 200, then the malware sends another GET request (Figure 10) with the following parameters (Figure 11).

Format = "?e=%d&&t=%d&&k=%d"

Figure 10: Second GET request

Figure 11: Second GET request parameters formation

Table 2 shows information about the parameters.

Table 2: Second GET request parameters

If the returned response is 200, the malware examines the Set-Cookie field. This field provides the Command ID. As shown in Figure 10, the field Set-Cookie responds with ID=17.

This Command ID acts as the index into a function table created by the malware. Figure 12 shows the creation of the virtual function table that will perform the backdoor’s command.

Figure 12: Function table

Table 3 shows the commands supported by HAWKBALL.

Table 3: HAWKBALL commands

Collect System Information

Command ID 17 indexes to a function that collects the system information and sends it to the C2 server. The system information includes:

• Computer Name
• User Name
• IP Address
• Active Code Page
• OEM Page
• OS Version
• Architecture Details (x32/x64)
• String at 0x68 offset from decrypted config file

This information is retrieved from the victim using the following WINAPI calls:

Format = "%s;%s;%s;%d;%d;%s;%s %dbit"

• GetComputerNameA
• GetUserNameA
• Gethostbyname and inet_ntoa
• GetACP
• GetOEMPC
• GetCurrentProcess and IsWow64Process

Figure 13: System information

The collected system information is concatenated together with a semicolon separating each field:

WIN732BIT-L-0;Administrator;10.128.62.115;1252;437;d0c;Windows 7 32bit

This information is encrypted using an XOR operation. The response from the second GET request is used as the encryption key. As shown in Figure 10, the second GET request responds with a 4-byte XOR key. In this case the key is 0xE5044C18.

Once encrypted, the system information is sent in the body of an HTTP POST. Figure 14 shows data sent over the network with the POST request.

Figure 14: POST request

In the request header, the field Cookie is set with the command ID of the command for which the response is sent. As shown in Figure 14, the Cookie field is set with ID=17, which is the response for the previous command. In the received response, the next command is returned in field Set-Cookie.

Table 4 shows the parameters of this POST request.

Table 4: POST request parameters

Create Process

The malware creates a process with specified arguments. Figure 15 shows the operation.

Figure 15: Command create process

Delete File

The malware deletes the file specified as an argument. Figure 16 show the operation.

Figure 16: Delete file operation

Get Directory Information

The malware gets information for the provided directory address using the following WINAPI calls:

• FindFirstFileW
• FindNextFileW
• FileTimeToLocalFileTime
• FiletimeToSystemTime

Figure 17 shows the API used for collecting information.

Figure 17: Get directory information

Get Disk Information

This command retrieves the drive information for drives C through Z along with available disk space for each drive.

Figure 18: Retrieve drive information

The information is stored in the following format for each drive:

Format = "%d+%d+%d+%d;"

Example: "8+512+6460870+16751103;"

The information for all the available drives is combined and sent to the server using an operation similar to Figure 14.

Anti-Debugging Tricks

Debugger Detection With PEB

The malware queries the value for the flag BeingDebugged from PEB to check whether the process is being debugged.

Figure 19: Retrieve value from PEB

NtQueryInformationProcess

The malware uses the NtQueryInformationProcess API to detect if it is being debugged. The following flags are used:

• Passing value 0x7 to ProcessInformationClass:

Figure 20: ProcessDebugPort verification

• Passing value 0x1E to ProcessInformationClass:

Figure 21: ProcessDebugFlags verification

• Passing value 0x1F to ProcessInformationClass:

Figure 22: ProcessDebugObject

Conclusion

HAWKBALL is a new backdoor that provides features attackers can use to collect information from a victim and deliver new payloads to the target. At the time of writing, the FireEye Multi-Vector Execution (MVX) engine is able to recognize and block this threat. We advise that all industries remain on alert, though, because the threat actors involved in this campaign may eventually broaden the scope of their current targeting.

Indicators of Compromise (IOC)

Network Indicators

• 149.28.182[.]78:443
• 149.28.182[.]78:80
• http://149.28.182[.]78/?t=0&&s=0&&p=wGH^69&&k=<tick_count>
• http://149.28.182[.]78/?e=0&&t=0&&k=<tick_count>
• http://149.28.182[.]78/?e=0&&t=<int_xor_key>&&k=<tick_count>
• Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; InfoPath.2)

FireEye Detections

Acknowledgement

Thank you to Matt Williams for providing reverse engineering support.