File name:

mkp_visual.exe

Full analysis: https://app.any.run/tasks/289a4213-0d09-40c9-a8b5-16f1f050d1a3
Verdict: Malicious activity
Threats:

Ransomware is a type of malicious software that locks users out of their system or data using different methods to force them to pay a ransom. Most often, such programs encrypt files on an infected machine and demand a fee to be paid in exchange for the decryption key. Additionally, such programs can be used to steal sensitive information from the compromised computer and even conduct DDoS attacks against affected organizations to pressure them into paying.

Analysis date: April 30, 2023, 14:17:22
OS: Windows 10 Professional (build: 19044, 64 bit)
Tags:
ransomware
Indicators:
MIME: application/x-dosexec
File info: PE32 executable (GUI) Intel 80386, for MS Windows
MD5:

F5F4A53ECF5FBDBD28D7F9F6E38C6C3D

SHA1:

D704B593395C4BE6340257D5E17EBAB7D07210B9

SHA256:

CA1D0D39322B9E941380C7FA66611FDA09D1EB35F069C69B2B8FE56ED8B38043

SSDEEP:

768:faQRff1B31aCytHLykiKPT3JATD2qBwV2ckjbnsb0Ah99De0YADNy0uri489CMn:faE318HxZATvnsblYOB99

ANY.RUN is an interactive service which provides full access to the guest system. Information in this report could be distorted by user actions and is provided for user acknowledgement as it is. ANY.RUN does not guarantee maliciousness or safety of the content.
  • MALICIOUS

    • Deletes shadow copies

      • cmd.exe (PID: 7072)
    • The DLL Hijacking

      • OfficeClickToRun.exe (PID: 6780)
    • Scans artifacts that could help determine the target

      • OfficeClickToRun.exe (PID: 6780)
    • Renames files like ransomware

      • mkp_visual.exe (PID: 7088)
  • SUSPICIOUS

    • Application launched itself

      • mkp_visual.exe (PID: 5568)
    • Reads the date of Windows installation

      • mkp_visual.exe (PID: 5568)
    • Starts CMD.EXE for commands execution

      • mkp_visual.exe (PID: 7088)
    • Executes as Windows Service

      • VSSVC.exe (PID: 6388)
      • wbengine.exe (PID: 964)
      • OfficeClickToRun.exe (PID: 6780)
      • vds.exe (PID: 1552)
    • Uses WMIC.EXE to obtain shadow copy information

      • cmd.exe (PID: 7072)
    • Creates files like ransomware instruction

      • mkp_visual.exe (PID: 7088)
    • Reads settings of System Certificates

      • OfficeClickToRun.exe (PID: 6780)
    • Checks Windows Trust Settings

      • OfficeClickToRun.exe (PID: 6780)
  • INFO

    • Process checks computer location settings

      • mkp_visual.exe (PID: 5568)
      • OfficeClickToRun.exe (PID: 6780)
    • The process checks LSA protection

      • mkp_visual.exe (PID: 5568)
      • mkp_visual.exe (PID: 7088)
      • vssadmin.exe (PID: 6572)
      • vdsldr.exe (PID: 6564)
      • VSSVC.exe (PID: 6388)
      • wbadmin.exe (PID: 6056)
      • wbengine.exe (PID: 964)
      • vds.exe (PID: 1552)
      • OfficeClickToRun.exe (PID: 6780)
      • WMIC.exe (PID: 5688)
    • Checks supported languages

      • mkp_visual.exe (PID: 5568)
      • mkp_visual.exe (PID: 7088)
      • OfficeClickToRun.exe (PID: 6780)
    • Reads the machine GUID from the registry

      • mkp_visual.exe (PID: 7088)
      • OfficeClickToRun.exe (PID: 6780)
      • mkp_visual.exe (PID: 5568)
    • Reads Windows Product ID

      • mkp_visual.exe (PID: 7088)
    • Reads the computer name

      • mkp_visual.exe (PID: 7088)
      • OfficeClickToRun.exe (PID: 6780)
      • mkp_visual.exe (PID: 5568)
    • Reads Microsoft Office registry keys

      • OfficeClickToRun.exe (PID: 6780)
    • Reads Environment values

      • OfficeClickToRun.exe (PID: 6780)
    • Reads CPU info

      • OfficeClickToRun.exe (PID: 6780)
    • Creates files in the program directory

      • mkp_visual.exe (PID: 7088)
Find more information about signature artifacts and mapping to MITRE ATT&CK™ MATRIX at the full report
No Malware configuration.

TRiD

.exe | Win32 Executable MS Visual C++ (generic) (42.2)
.exe | Win64 Executable (generic) (37.3)
.dll | Win32 Dynamic Link Library (generic) (8.8)
.exe | Win32 Executable (generic) (6)
.exe | Generic Win/DOS Executable (2.7)

EXIF

EXE

Subsystem: Windows GUI
SubsystemVersion: 4
ImageVersion: -
OSVersion: 4
EntryPoint: 0x6800
UninitializedDataSize: -
InitializedDataSize: 99328
CodeSize: 32768
LinkerVersion: 8
PEType: PE32
ImageFileCharacteristics: No relocs, Executable, 32-bit
TimeStamp: 2022:12:31 21:31:22+00:00
MachineType: Intel 386 or later, and compatibles

Summary

Architecture: IMAGE_FILE_MACHINE_I386
Subsystem: IMAGE_SUBSYSTEM_WINDOWS_GUI
Compilation Date: 31-Dec-2022 21:31:22

DOS Header

Magic number: MZ
Bytes on last page of file: 0x0090
Pages in file: 0x0003
Relocations: 0x0000
Size of header: 0x0004
Min extra paragraphs: 0x0000
Max extra paragraphs: 0xFFFF
Initial SS value: 0x0000
Initial SP value: 0x00B8
Checksum: 0x0000
Initial IP value: 0x0000
Initial CS value: 0x0000
Overlay number: 0x0000
OEM identifier: 0x0000
OEM information: 0x0000
Address of NE header: 0x000000E0

PE Headers

Signature: PE
Machine: IMAGE_FILE_MACHINE_I386
Number of sections: 5
Time date stamp: 31-Dec-2022 21:31:22
Pointer to Symbol Table: 0x00000000
Number of symbols: 0
Size of Optional Header: 0x00E0
Characteristics:
  • IMAGE_FILE_32BIT_MACHINE
  • IMAGE_FILE_EXECUTABLE_IMAGE
  • IMAGE_FILE_RELOCS_STRIPPED

Sections

Name
Virtual Address
Virtual Size
Raw Size
Charateristics
Entropy
.text
0x00001000
0x00007F64
0x00008000
IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ
6.4072
.rdata
0x00009000
0x00000F5A
0x00001000
IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ
5.09295
.data
0x0000A000
0x000142BC
0x00000000
IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE
0
.ndata
0x0001F000
0x00002BA1
0x00002C00
IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE
7.97617
.rsrc
0x00022000
0x000002F8
0x00000400
IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ
2.3243

Resources

Title
Entropy
Size
Codepage
Language
Type
101
3.11363
660
UNKNOWN
UNKNOWN
RT_DIALOG

Imports

ADVAPI32.dll
GDI32.dll
KERNEL32.dll
MPR.dll
MSIMG32.dll
SHELL32.dll
USER32.dll
ole32.dll
No data.
screenshotscreenshotscreenshotscreenshotscreenshot
All screenshots are available in the full report
All screenshots are available in the full report
Total processes
139
Monitored processes
12
Malicious processes
4
Suspicious processes
0

Behavior graph

Click at the process to see the details
start mkp_visual.exe no specs mkp_visual.exe cmd.exe no specs conhost.exe no specs vssadmin.exe no specs vssvc.exe no specs wbadmin.exe wbengine.exe no specs vdsldr.exe no specs vds.exe no specs wmic.exe no specs officeclicktorun.exe

Process information

PID
CMD
Path
Indicators
Parent process
964"C:\WINDOWS\system32\wbengine.exe"C:\Windows\System32\wbengine.exeservices.exe
User:
SYSTEM
Company:
Microsoft Corporation
Integrity Level:
SYSTEM
Description:
Microsoft® Block Level Backup Engine Service EXE
Exit code:
0
Version:
10.0.19041.1 (WinBuild.160101.0800)
Modules
Images
c:\windows\system32\ntdll.dll
c:\windows\system32\wbengine.exe
c:\windows\system32\kernel32.dll
c:\windows\system32\kernelbase.dll
c:\windows\system32\advapi32.dll
c:\windows\system32\msvcrt.dll
c:\windows\system32\sechost.dll
c:\windows\system32\rpcrt4.dll
c:\windows\system32\user32.dll
c:\windows\system32\win32u.dll
1552C:\WINDOWS\System32\vds.exeC:\Windows\System32\vds.exeservices.exe
User:
SYSTEM
Company:
Microsoft Corporation
Integrity Level:
SYSTEM
Description:
Virtual Disk Service
Exit code:
0
Version:
10.0.19041.1 (WinBuild.160101.0800)
Modules
Images
c:\windows\system32\vds.exe
c:\windows\system32\ntdll.dll
c:\windows\system32\kernel32.dll
c:\windows\system32\kernelbase.dll
c:\windows\system32\user32.dll
c:\windows\system32\win32u.dll
c:\windows\system32\gdi32.dll
c:\windows\system32\gdi32full.dll
c:\windows\system32\msvcp_win.dll
c:\windows\system32\ucrtbase.dll
5568"C:\Users\admin\Desktop\mkp_visual.exe" C:\Users\admin\Desktop\mkp_visual.exeexplorer.exe
User:
admin
Integrity Level:
MEDIUM
Exit code:
0
Modules
Images
c:\users\admin\desktop\mkp_visual.exe
c:\windows\system32\ntdll.dll
c:\windows\syswow64\ntdll.dll
c:\windows\system32\wow64.dll
c:\windows\system32\wow64win.dll
c:\windows\system32\wow64cpu.dll
c:\windows\syswow64\kernel32.dll
c:\windows\syswow64\kernelbase.dll
c:\windows\syswow64\apphelp.dll
c:\windows\syswow64\win32u.dll
5688wmic shadowcopy deleteC:\Windows\System32\wbem\WMIC.execmd.exe
User:
admin
Company:
Microsoft Corporation
Integrity Level:
HIGH
Description:
WMI Commandline Utility
Exit code:
0
Version:
10.0.19041.1 (WinBuild.160101.0800)
Modules
Images
c:\windows\system32\wbem\wmic.exe
c:\windows\system32\ntdll.dll
c:\windows\system32\kernel32.dll
c:\windows\system32\kernelbase.dll
c:\windows\system32\apphelp.dll
c:\windows\system32\msvcrt.dll
c:\windows\system32\iphlpapi.dll
c:\windows\system32\framedynos.dll
c:\windows\system32\combase.dll
c:\windows\system32\ucrtbase.dll
6056wbadmin delete catalog -quietC:\Windows\System32\wbadmin.exe
cmd.exe
User:
admin
Company:
Microsoft Corporation
Integrity Level:
HIGH
Description:
Command Line Interface for Microsoft® BLB Backup
Exit code:
0
Version:
10.0.19041.1 (WinBuild.160101.0800)
Modules
Images
c:\windows\system32\wbadmin.exe
c:\windows\system32\ntdll.dll
c:\windows\system32\kernel32.dll
c:\windows\system32\kernelbase.dll
c:\windows\system32\apphelp.dll
c:\windows\system32\advapi32.dll
c:\windows\system32\msvcrt.dll
c:\windows\system32\sechost.dll
c:\windows\system32\rpcrt4.dll
c:\windows\system32\ole32.dll
6388C:\WINDOWS\system32\vssvc.exeC:\Windows\System32\VSSVC.exeservices.exe
User:
SYSTEM
Company:
Microsoft Corporation
Integrity Level:
SYSTEM
Description:
Microsoft® Volume Shadow Copy Service
Exit code:
0
Version:
10.0.19041.1 (WinBuild.160101.0800)
Modules
Images
c:\windows\system32\vssvc.exe
c:\windows\system32\ntdll.dll
c:\windows\system32\kernel32.dll
c:\windows\system32\kernelbase.dll
c:\windows\system32\msvcrt.dll
c:\windows\system32\oleaut32.dll
c:\windows\system32\msvcp_win.dll
c:\windows\system32\ucrtbase.dll
c:\windows\system32\combase.dll
c:\windows\system32\rpcrt4.dll
6564C:\WINDOWS\System32\vdsldr.exe -EmbeddingC:\Windows\System32\vdsldr.exesvchost.exe
User:
SYSTEM
Company:
Microsoft Corporation
Integrity Level:
SYSTEM
Description:
Virtual Disk Service Loader
Exit code:
0
Version:
10.0.19041.1202 (WinBuild.160101.0800)
Modules
Images
c:\windows\system32\ntdll.dll
c:\windows\system32\vdsldr.exe
c:\windows\system32\kernel32.dll
c:\windows\system32\kernelbase.dll
c:\windows\system32\advapi32.dll
c:\windows\system32\msvcrt.dll
c:\windows\system32\sechost.dll
c:\windows\system32\rpcrt4.dll
c:\windows\system32\user32.dll
c:\windows\system32\win32u.dll
6572vssadmin delete shadows /all /quietC:\Windows\System32\vssadmin.execmd.exe
User:
admin
Company:
Microsoft Corporation
Integrity Level:
HIGH
Description:
Command Line Interface for Microsoft® Volume Shadow Copy Service
Exit code:
0
Version:
10.0.19041.1 (WinBuild.160101.0800)
Modules
Images
c:\windows\system32\ntdll.dll
c:\windows\system32\vssadmin.exe
c:\windows\system32\kernel32.dll
c:\windows\system32\kernelbase.dll
c:\windows\system32\apphelp.dll
c:\windows\system32\advapi32.dll
c:\windows\system32\msvcrt.dll
c:\windows\system32\sechost.dll
c:\windows\system32\rpcrt4.dll
c:\windows\system32\combase.dll
6780"C:\Program Files\Common Files\Microsoft Shared\ClickToRun\OfficeClickToRun.exe" /serviceC:\Program Files\Common Files\microsoft shared\ClickToRun\OfficeClickToRun.exe
services.exe
User:
SYSTEM
Company:
Microsoft Corporation
Integrity Level:
SYSTEM
Description:
Microsoft Office Click-to-Run (SxS)
Exit code:
0
Version:
16.0.16026.20140
Modules
Images
c:\program files\common files\microsoft shared\clicktorun\officeclicktorun.exe
c:\windows\system32\ntdll.dll
c:\windows\system32\kernel32.dll
c:\windows\system32\kernelbase.dll
c:\windows\system32\advapi32.dll
c:\windows\system32\msvcrt.dll
c:\windows\system32\sechost.dll
c:\windows\system32\rpcrt4.dll
c:\windows\system32\gdi32.dll
c:\windows\system32\win32u.dll
7024\??\C:\WINDOWS\system32\conhost.exe 0xffffffff -ForceV1C:\Windows\System32\conhost.execmd.exe
User:
admin
Company:
Microsoft Corporation
Integrity Level:
HIGH
Description:
Console Window Host
Exit code:
0
Version:
10.0.19041.1 (WinBuild.160101.0800)
Modules
Images
c:\windows\system32\conhost.exe
c:\windows\system32\ntdll.dll
c:\windows\system32\kernel32.dll
c:\windows\system32\kernelbase.dll
c:\windows\system32\msvcp_win.dll
c:\windows\system32\ucrtbase.dll
c:\windows\system32\shcore.dll
c:\windows\system32\msvcrt.dll
c:\windows\system32\combase.dll
c:\windows\system32\rpcrt4.dll
Total events
2 982
Read events
2 932
Write events
46
Delete events
4

Modification events

(PID) Process:(5568) mkp_visual.exeKey:HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap
Operation:writeName:ProxyBypass
Value:
1
(PID) Process:(5568) mkp_visual.exeKey:HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap
Operation:writeName:IntranetName
Value:
1
(PID) Process:(5568) mkp_visual.exeKey:HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap
Operation:writeName:UNCAsIntranet
Value:
1
(PID) Process:(5568) mkp_visual.exeKey:HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap
Operation:writeName:AutoDetect
Value:
0
(PID) Process:(6780) OfficeClickToRun.exeKey:HKEY_USERS\.DEFAULT\Software\Microsoft\Office\16.0\Common\LanguageResources\EnabledEditingLanguages
Operation:writeName:en-US
Value:
1
(PID) Process:(6780) OfficeClickToRun.exeKey:HKEY_USERS\.DEFAULT\Software\Microsoft\Office\16.0\Common\LanguageResources\EnabledEditingLanguages
Operation:writeName:en-US
Value:
2
(PID) Process:(6780) OfficeClickToRun.exeKey:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\Windows Error Reporting\RuntimeExceptionHelperModules
Operation:writeName:C:\Program Files\Common Files\Microsoft Shared\ClickToRun\c2r64werhandler.dll
Value:
0
(PID) Process:(6780) OfficeClickToRun.exeKey:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun
Operation:writeName:MachineMetadataSentTime
Value:
13320426467868
(PID) Process:(6780) OfficeClickToRun.exeKey:HKEY_USERS\.DEFAULT\Software\Microsoft\Office\16.0\Common
Operation:writeName:SessionId
Value:
9145FDD7A74A4049973198598B611657
(PID) Process:(6780) OfficeClickToRun.exeKey:HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap
Operation:writeName:ProxyBypass
Value:
1
Executable files
20
Suspicious files
2 212
Text files
186
Unknown types
0

Dropped files

PID
Process
Filename
Type
7088mkp_visual.exeC:\Users\admin\Desktop\includesedit.rtf.[C8E7DCE6].[keydecryptcomp@outlook.com].mkpbinary
MD5:449E32B8C41148EC9B6EDDA8948395ED
SHA256:48F1E0B48F55B37F54876C0AC3F9F7C7A63A542119AD1909422278C90791D59B
7088mkp_visual.exeC:\Users\admin\Desktop\fullyfield.rtf.[C8E7DCE6].[keydecryptcomp@outlook.com].mkpbinary
MD5:D74F0CF03816CD5367066FC34B23408E
SHA256:216017A6E91893B754FF577B87F9BCE80E7426F810D81F52C9B250DD2A73B465
7088mkp_visual.exeC:\Users\admin\Desktop\fullyfield.rtfbinary
MD5:D74F0CF03816CD5367066FC34B23408E
SHA256:216017A6E91893B754FF577B87F9BCE80E7426F810D81F52C9B250DD2A73B465
7088mkp_visual.exeC:\found.000\dir0000.chk\UpdateSessionOrchestration.016.etlbinary
MD5:56D2962570886A7B38FD9C9BEBC127F4
SHA256:B6C8348060EB611E56350EAD38B6C75EAF29C0F5329FAF9E07D78703AF365AFD
7088mkp_visual.exeC:\Users\admin\Desktop\viasubmit.jpg.[C8E7DCE6].[keydecryptcomp@outlook.com].mkpbinary
MD5:CA18BCE78D68281A7B29226C91D05432
SHA256:8730D9E649C2BA5581DE5303A926EA5BA7B3AFE7ED0F2951612707AD281192A7
7088mkp_visual.exeC:\found.000\dir0000.chk\UpdateSessionOrchestration.016.etl.[C8E7DCE6].[keydecryptcomp@outlook.com].mkpbinary
MD5:56D2962570886A7B38FD9C9BEBC127F4
SHA256:B6C8348060EB611E56350EAD38B6C75EAF29C0F5329FAF9E07D78703AF365AFD
7088mkp_visual.exeC:\Users\admin\Desktop\viasubmit.jpgbinary
MD5:CA18BCE78D68281A7B29226C91D05432
SHA256:8730D9E649C2BA5581DE5303A926EA5BA7B3AFE7ED0F2951612707AD281192A7
7088mkp_visual.exeC:\Users\admin\Desktop\+README-WARNING+.txttext
MD5:76D1F1E96D052F00CD69899442DDDAC0
SHA256:92DA8539BA1DB077255CF00E93E91E5AF3DE4B53ACB20B695DA69903532BB4D3
7088mkp_visual.exeC:\Users\admin\Desktop\pophold.rtf.[C8E7DCE6].[keydecryptcomp@outlook.com].mkpbinary
MD5:9C48F8363421647325458B4D394FF29F
SHA256:C5657CC4FA1D0E4D041FE88FC321BAF1C653C120E55A53A229CC77846F9A37AF
7088mkp_visual.exeC:\Users\admin\Desktop\pophold.rtfbinary
MD5:9C48F8363421647325458B4D394FF29F
SHA256:C5657CC4FA1D0E4D041FE88FC321BAF1C653C120E55A53A229CC77846F9A37AF
Download PCAP, analyze network streams, HTTP content and a lot more at the full report
HTTP(S) requests
2
TCP/UDP connections
17
DNS requests
11
Threats
0

HTTP requests

PID
Process
Method
HTTP Code
IP
URL
CN
Type
Size
Reputation
5616
SIHClient.exe
GET
200
88.221.169.152:80
http://www.microsoft.com/pkiops/crl/Microsoft%20ECC%20Product%20Root%20Certificate%20Authority%202018.crl
unknown
binary
418 b
whitelisted
5616
SIHClient.exe
GET
200
88.221.169.152:80
http://www.microsoft.com/pkiops/crl/Microsoft%20ECC%20Update%20Secure%20Server%20CA%202.1.crl
unknown
binary
409 b
whitelisted
Download PCAP, analyze network streams, HTTP content and a lot more at the full report

Connections

PID
Process
IP
Domain
ASN
CN
Reputation
51.124.78.146:443
MICROSOFT-CORP-MSN-AS-BLOCK
NL
whitelisted
5756
svchost.exe
20.190.160.17:443
MICROSOFT-CORP-MSN-AS-BLOCK
NL
whitelisted
5952
MoUsoCoreWorker.exe
51.124.78.146:443
MICROSOFT-CORP-MSN-AS-BLOCK
NL
whitelisted
5616
SIHClient.exe
88.221.169.152:80
www.microsoft.com
AKAMAI-AS
DE
whitelisted
20.190.160.17:443
MICROSOFT-CORP-MSN-AS-BLOCK
NL
whitelisted
5616
SIHClient.exe
20.166.126.56:443
fe3cr.delivery.mp.microsoft.com
MICROSOFT-CORP-MSN-AS-BLOCK
IE
whitelisted
5756
svchost.exe
20.190.160.20:443
MICROSOFT-CORP-MSN-AS-BLOCK
NL
whitelisted
5616
SIHClient.exe
20.12.23.50:443
slscr.update.microsoft.com
MICROSOFT-CORP-MSN-AS-BLOCK
US
whitelisted
20.190.160.20:443
MICROSOFT-CORP-MSN-AS-BLOCK
NL
whitelisted
6712
slui.exe
40.91.76.224:443
activation-v2.sls.microsoft.com
MICROSOFT-CORP-MSN-AS-BLOCK
US
whitelisted

DNS requests

Domain
IP
Reputation
officeclient.microsoft.com
  • 52.109.32.24
whitelisted
ecs.office.com
  • 52.113.194.132
whitelisted
self.events.data.microsoft.com
  • 20.189.173.13
whitelisted
slscr.update.microsoft.com
  • 20.12.23.50
whitelisted
www.microsoft.com
  • 88.221.169.152
whitelisted
fe3cr.delivery.mp.microsoft.com
  • 20.166.126.56
whitelisted
activation-v2.sls.microsoft.com
  • 40.91.76.224
whitelisted

Threats

No threats detected
Process
Message
wbadmin.exe
Invalid parameter passed to C runtime function.
wbadmin.exe
Invalid parameter passed to C runtime function.