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No funky IOCTL just a plain unsafe call to CreateProcess().In detail, the scheduler (sched. exe) running with SYSTEM privileges calls the CreateProcess() API without enclosing lpCommandLine in quotes to regularly shell avwsc.exe
Calling an executable with a path has spaces in it and not using quotes will trigger windows to search for the executable in various areas.
Calling for instance -
c:\program files\avira\antivir PersonalEdition Classic\avwsc.exe,
will first look for
This is documented and intended behaviour as can be seen at :
Quoting ms682425.aspx :
The lpApplicationName parameter can be NULL. In that case, the module name must be the first white space–delimited token in the lpCommandLine string. If you are using a long file name that contains a space, use quoted strings to
indicate where the file name ends and the arguments begin; otherwise, the file name is ambiguous. For example, consider the string "c:\program files\sub dir\program name". This string can be interpreted in a number of ways. The system tries to interpret the possibilities in the following order:
c:\program.exe files\sub dir\program name, c:\program files\sub.exe dir\program name
c:\program files\sub dir\program.exe name, c:\program files\sub dir\program name.exe
Pre-conditions for a CreateProcess() call to be insecure :
- lpApplicationName contains a NULL
- the path in lpCommandLine contains white space
- the path in lpCommandLine is not enclosed in quotation marks
- Elevation of privileges to SYSTEM is possible by writing the payload to c:\program files\avira\antivir.exe
- Autostart vector - The payload will be executed even after a reboot
IV. Disclosure Timeline
with there next Emergency Update (EU2)
If the string does not specify a path, the function uses a
standard search strategy to find the file.