Windows Prefetch File Format

From ForensicsWiki
Revision as of 10:37, 20 January 2012 by Athulin (Talk | contribs) (Section D)

Jump to: navigation, search

A Windows Prefetch file consists of one file header and multiple file sections with different content. Not all content has an obvious forensic value.

As far as have been possible to ascertain, there is no public description of the format. The description below has been synthesised from examination of multiple prefetch files.


This format has been observed on Windows XP, ... will need to be modified for Vista/Win7 format

Field Offset Length Type Notes
H1 0x0000 4 DWORD  ? Probably a version number, identifying the file structure. Observed values: 0x11 - Windows XP; 0x17 - Vista, Windows 7
H2 0x0004 4 DWORD  ? Probably a file magic number. Only observed value: 0x41434353 ('SCCA')
H3 0x0008 4 DWORD?  ? Observed values: 0x0F - Windows XP, 0x11 - Windows 7
H4 0x000C 4 DWORD Prefetch file length.
H5 0x0010 60 USTR Name of executable as Unicode string, truncated after character 29 if necessary, and terminated by U+0000. As it appears in the prefetch file file name.
H6 0x004C 4 DWORD The prefetch hash, as it appears in the pf file name.
H7 0x0050 4 ? ? Observed values: 0 for almost all prefetch files (XP); 1 for (XP)
H8 0x0054 4 DWORD Offset to section A
H9 0x0058 4 DWORD  ? Nr of entries in section A
H10 0x005C 4 DWORD Offset to section B
H11 0x0060 4 DWORD Nr of entries in section B
H12 0x0064 4 DWORD Offset to section C
H13 0x0068 4 DWORD Length of section C
H14 0x006C 4 DWORD Offset to section D
H15 0x0070 4 DWORD  ? Probably the number of entries in the D section header
H16 0x0074 4 DWORD Length of section D
H17 0x0078 8 FTIME Latest execution time of executable (FILETIME)
H18 0x0080 16  ?  ? Possibly structured as 4 DWORD. Observed values: /0x00000000 0x00000000 0x00000000 0x00000000/, /0x47868c00 0x00000000 0x47860c00 0x00000000/
H19 0x0090 4 DWORD Execution counter
H20 0x0094 4 DWORD?  ? Observed values: 1, 2, 3, 4, 5, 6 (XP)

It's worth noting that the name of a carved prefetch file can be restored using the information in field H5 and H6, and its size can be determined by field H4.

Section A and B

The content of these two sections is unknown.

Section C

Section D

Section D contains one or more subsections. The number is (most likely) determined by the DWORD at file offset 0x0070. Each subsection refers to directories on an identified volume.

In this section, all offsets are assumed to be counted from the start of the D section.

Field Offset Length Type Notes
DH1 +0x0000 4 DWORD Offset to volume string (Unicode, terminated by U+0000)
DH2 +0x0004 4 DWORD Length of volume string (nr of characters, including terminating U+0000)
DH3 +0x0008 8 FTIME (File time)
DH4 +0x0010 4 DWORD Volume serial number of volume indicated by volume string
DH5 +0x0014 4 DWORD  ? Offset to section DHS1
DH6 +0x0018 4 DWORD  ? Length of section DHS1 (in bytes)
DH7 +0x001C 4 DWORD  ? Offset to section DHS2
DH8 +0x0020 4 DWORD  ? Nr of strings in section DHS2
 ? +0x0024  ?  ?  ? additional 28 bytes (includes one timestamp?)

If all the executables and libraries referenced in the C section are from one single disk volume, there will be only one section in the D section. If multiple volumes are referenced by section C, section D will contain multiple sections. (A simple way to force this situation is to copy, say, NOTEPAD.EXE to a USB drive, and start it from that volume. The corresponding prefetch file will have one D header referring to, e.g. \DEVICE\HARDDISK1\DP(1)0-0+4 (the USB drive), and one to, e.g. \DEVICE\HARDDISKVOLUME1\ (where the .DLLs and other support files were found).