Difference between revisions of "Windows Prefetch File Format"

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A Windows Prefetch file consists of one file header and multiple file sections with different content. Not all content has an obvious forensic value.
 
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
 
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.  
+
of multiple prefetch files.
 +
 
 +
== Characteristics ==
 +
Integer values are stored in little-endian.
 +
 
 +
Strings are stored as [http://en.wikipedia.org/wiki/UTF-16/UCS-2 UTF-16 little-endian] without a byte-order-mark (BOM).
  
== Header ==
+
Timestamps are stored as [http://msdn2.microsoft.com/en-us/library/ms724284.aspx Windows FILETIME] in UTC.
  
This format has been observed on Windows XP, ...  will need to be modified for Vista/Win7 format
+
== File header ==
  
 
{| class="wikitable"
 
{| class="wikitable"
Line 20: Line 27:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| ? Probably a version number, identifying the file structure. Observed values: 0x11 - Windows XP; 0x17 - Vista, Windows 7
+
| Format version (see format version section below)
 
|-
 
|-
 
| H2
 
| H2
Line 26: Line 33:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| ? Probably a file magic number. Only observed value: 0x41434353 ('SCCA')
+
| Signature 'SCCA' (or in hexadecimal representation 0x53 0x43 0x43 0x4)
 
|-
 
|-
 
| H3
 
| H3
Line 32: Line 39:
 
| 4
 
| 4
 
| DWORD?
 
| DWORD?
| ? Observed values: 0x0F - Windows XP, 0x11 - Windows 7
+
| Unknown - Values observed: 0x0F - Windows XP, 0x11 - Windows 7, Windows 8.1
 
|-
 
|-
 
| H4
 
| H4
Line 38: Line 45:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| Prefetch file length.
+
| Prefetch file size (or length) (sometimes referred to as End of File (EOF)).
 
|-
 
|-
 
| H5
 
| H5
Line 44: Line 51:
 
| 60
 
| 60
 
| USTR
 
| USTR
| Name of executable as Unicode string, truncated after 29 code units, if necessary, and terminated by U+0000. As it appears in the prefetch file file name.
+
| The name of the (original) executable as a Unicode (UTF-16 litte-endian string), up to 29 characters and terminated by an end-of-string character (U+0000). This name should correspond with the one in the prefetch file filename.
 
|-
 
|-
 
| H6
 
| H6
Line 50: Line 57:
 
|4
 
|4
 
|DWORD
 
|DWORD
|The prefetch hash, as it appears in the pf file name.
+
|The prefetch hash. This hash value should correspond with the one in the prefetch file filename.
 
|-
 
|-
 
| H7
 
| H7
Line 56: Line 63:
 
|4
 
|4
 
|?
 
|?
|? Observed values: 0 for almost all prefetch files (XP); 1 for NTOSBOOT-B00DFAAD.pf (XP)
+
| Unknown (flags)? Values observed: 0 for almost all prefetch files (XP); 1 for NTOSBOOT-B00DFAAD.pf (XP)
 +
|-
 +
|}
 +
 
 +
=== Format version ===
 +
 
 +
{| class="wikitable"
 +
|-
 +
! Value
 +
! Windows version
 +
|-
 +
| 17 (0x11)
 +
| Windows XP, Windows 2003
 +
|-
 +
| 23 (0x17)
 +
| Windows Vista, Windows 7
 +
|-
 +
| 26 (0x1a)
 +
| Windows 8.1 (note this could be Windows 8 as well but has not been confirmed)
 +
|-
 +
|}
 +
 
 +
=== File information - version 17 ===
 +
 
 +
The following part of the file header is version dependent. It is sometime considered part of the file header. Below the structure for format version 17.
 +
 
 +
{| class="wikitable"
 +
|-
 +
! Field
 +
! Offset
 +
! Length
 +
! Type
 +
! Notes
 
|-
 
|-
 
| H8
 
| H8
Line 62: Line 101:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| Offset to section A
+
| The offset to section A. The offset is relative from the start of the file.
 
|-
 
|-
 
| H9
 
| H9
Line 68: Line 107:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| ? Nr of entries in section A
+
| The number of entries in section A.
 
|-
 
|-
 
| H10
 
| H10
Line 74: Line 113:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| Offset to section B
+
| The offset to section B. The offset is relative from the start of the file.
 
|-
 
|-
 
| H11
 
| H11
Line 80: Line 119:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| Nr of entries in section B
+
| The number of entries in section B.
 
|-
 
|-
 
| H12
 
| H12
Line 86: Line 125:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| Offset to section C
+
| The offset to section C. The offset is relative from the start of the file.
 
|-
 
|-
 
| H13
 
| H13
Line 92: Line 131:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| Length of section C
+
| Length of section C.
 
|-
 
|-
 
| H14
 
| H14
Line 98: Line 137:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| Offset to section D
+
| Offset to section D. The offset is relative from the start of the file.
 
|-
 
|-
 
| H15
 
| H15
Line 104: Line 143:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| ? Probably the number of entries in the D section header
+
| Unknown ? (Previously opted: Probably the number of entries in the D section header.)
 
|-
 
|-
 
| H16
 
| H16
Line 110: Line 149:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| Length of section D
+
| Unknown ? (Previously opted: Length of section D)
 
|-
 
|-
 
| H17
 
| H17
Line 116: Line 155:
 
| 8
 
| 8
 
| FTIME
 
| FTIME
| Latest execution time of executable (FILETIME)
+
| Latest execution time (or run time) of executable (FILETIME)
 
|-
 
|-
 
| H18
 
| H18
Line 122: Line 161:
 
| 16
 
| 16
 
| ?
 
| ?
| ? Possibly structured as 4 DWORD. Observed values: /0x00000000 0x00000000 0x00000000 0x00000000/, /0x47868c00 0x00000000 0x47860c00 0x00000000/
+
| Unknown ? Possibly structured as 4 DWORD. Observed values: /0x00000000 0x00000000 0x00000000 0x00000000/, /0x47868c00 0x00000000 0x47860c00 0x00000000/ (don't exclude the possibility here that this is remnant data)
 
|-
 
|-
 
| H19
 
| H19
Line 128: Line 167:
 
| 4
 
| 4
 
| DWORD
 
| DWORD
| Execution counter
+
| Execution counter (or run count)
 
|-
 
|-
 
| H20
 
| H20
Line 134: Line 173:
 
| 4
 
| 4
 
| DWORD?
 
| DWORD?
| ? Observed values: 1, 2, 3, 4, 5, 6 (XP)
+
| Unknown ? Observed values: 1, 2, 3, 4, 5, 6 (XP)
 
|-
 
|-
 
|}
 
|}
Line 140: Line 179:
 
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.
 
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 ==
+
== Section A ==
 +
This section contains an array with 20 byte (version 17) or 32 byte (version 23 and 26) entry records.
  
The content of these two sections is unknown.
+
The actual format and usage of these entry records is currently not known.
 +
 
 +
== Section B ==
 +
This section contains an array with 12 byte (version 17, 23 and 26) entry records.
 +
 
 +
The actual format and usage of these entry records is currently not known.
  
 
== Section C ==
 
== Section C ==
 +
This section contains an array of UTF-16 little-endian formatted strings with end-of-string characters (U+0000).
  
== Section D ==
+
At the end of the section there seems to be alignment padding that can contain remnant values.
 +
 
 +
== Section D - Volume information (block) ==
  
 
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.
 
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.
 
In this section, all offsets are assumed to be counted from the start of the D section.
 +
 +
=== Volume information - version 17 ===
 +
The following values are version dependent. Below the structure for format version 17.
  
 
{| class="wikitable"
 
{| class="wikitable"
Line 175: Line 226:
 
| +0x0008
 
| +0x0008
 
| 8
 
| 8
| FTIME
+
| FILETIME
| (File time)
+
| Volume creation time.
 
|-
 
|-
 
| DH4
 
| DH4
Line 215: Line 266:
 
|}
 
|}
  
 +
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).
  
 +
== See Also ==
 +
* [[Prefetch]]
  
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).
+
== External Links ==
 +
* [https://googledrive.com/host/0B3fBvzttpiiSbl9XZGZzQ05hZkU/Windows%20Prefetch%20File%20(PF)%20format.pdf Windows Prefetch File (PF) format], by the [[libssca|libssca project]]
 +
 
 +
[[Category:File Formats]]

Revision as of 01:11, 30 January 2014

Information icon.png

Please help to improve this article by expanding it.
Further information might be found on the discussion page.

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.

Characteristics

Integer values are stored in little-endian.

Strings are stored as UTF-16 little-endian without a byte-order-mark (BOM).

Timestamps are stored as Windows FILETIME in UTC.

File header

Field Offset Length Type Notes
H1 0x0000 4 DWORD Format version (see format version section below)
H2 0x0004 4 DWORD Signature 'SCCA' (or in hexadecimal representation 0x53 0x43 0x43 0x4)
H3 0x0008 4 DWORD? Unknown - Values observed: 0x0F - Windows XP, 0x11 - Windows 7, Windows 8.1
H4 0x000C 4 DWORD Prefetch file size (or length) (sometimes referred to as End of File (EOF)).
H5 0x0010 60 USTR The name of the (original) executable as a Unicode (UTF-16 litte-endian string), up to 29 characters and terminated by an end-of-string character (U+0000). This name should correspond with the one in the prefetch file filename.
H6 0x004C 4 DWORD The prefetch hash. This hash value should correspond with the one in the prefetch file filename.
H7 0x0050 4 ? Unknown (flags)? Values observed: 0 for almost all prefetch files (XP); 1 for NTOSBOOT-B00DFAAD.pf (XP)

Format version

Value Windows version
17 (0x11) Windows XP, Windows 2003
23 (0x17) Windows Vista, Windows 7
26 (0x1a) Windows 8.1 (note this could be Windows 8 as well but has not been confirmed)

File information - version 17

The following part of the file header is version dependent. It is sometime considered part of the file header. Below the structure for format version 17.

Field Offset Length Type Notes
H8 0x0054 4 DWORD The offset to section A. The offset is relative from the start of the file.
H9 0x0058 4 DWORD The number of entries in section A.
H10 0x005C 4 DWORD The offset to section B. The offset is relative from the start of the file.
H11 0x0060 4 DWORD The number of entries in section B.
H12 0x0064 4 DWORD The offset to section C. The offset is relative from the start of the file.
H13 0x0068 4 DWORD Length of section C.
H14 0x006C 4 DWORD Offset to section D. The offset is relative from the start of the file.
H15 0x0070 4 DWORD Unknown ? (Previously opted: Probably the number of entries in the D section header.)
H16 0x0074 4 DWORD Unknown ? (Previously opted: Length of section D)
H17 0x0078 8 FTIME Latest execution time (or run time) of executable (FILETIME)
H18 0x0080 16  ? Unknown ? Possibly structured as 4 DWORD. Observed values: /0x00000000 0x00000000 0x00000000 0x00000000/, /0x47868c00 0x00000000 0x47860c00 0x00000000/ (don't exclude the possibility here that this is remnant data)
H19 0x0090 4 DWORD Execution counter (or run count)
H20 0x0094 4 DWORD? Unknown ? 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

This section contains an array with 20 byte (version 17) or 32 byte (version 23 and 26) entry records.

The actual format and usage of these entry records is currently not known.

Section B

This section contains an array with 12 byte (version 17, 23 and 26) entry records.

The actual format and usage of these entry records is currently not known.

Section C

This section contains an array of UTF-16 little-endian formatted strings with end-of-string characters (U+0000).

At the end of the section there seems to be alignment padding that can contain remnant values.

Section D - Volume information (block)

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.

Volume information - version 17

The following values are version dependent. Below the structure for format version 17.

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 FILETIME Volume creation 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).

See Also

External Links