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A Python script to parse the NTFS USN journal

Project description

Python script to parse the NTFS USN Journal

Description

The NTFS USN journal is a volume-specific file which essentially logs changes to files and file metadata. As such, it can be a treasure trove of information during DFIR investigations. The change journal is located at $Extend$UsnJrnl:$J and can be easily extracted using Encase or FTK.

usn.py is a script written in Python which parses the journal - and has what I consider to be a couple of unique features.

Default Output

With no command-line options set, usn.py will produce USN journal records in the format below:

dev@computer:$ python usn.py usnJRNL
2015-10-09 21:44:39.003402 | msctfui.dll | FILE_CREATE

Command-Line Options

positional arguments:
  journal               Parse the specified USN journal
optional arguments:
  -h, --help            show this help message and exit
  -c, --csv             Return USN records in comma-separated format
  -f FILENAME, --filename FILENAME
                        Returns USN record matching a given filename
  -i, --info            Returns information about the USN Journal file itself
  -l LAST, --last LAST  Return all USN records for the last n days
  -q, --quick           Parse a large journal file quickly
  -v, --verbose         Return all USN properties

–info

The USN Journal is a Sparse File. A large-ish USN change journal can contain gigabytes and gigabytes of leading NULL bytes. Sometimes a large journal file doesn’t even contain that many USN records. Using the –info / -i switch prints high-level information about the USN journal itself.

dev@computer:~$python usn.py usnJRNL --info
[ + ] File size (bytes): 57118079632
[ + ] Leading null bytes consume ~99% of the journal file
[ + ] Pointer to first USN record: 57082904576
[ + ] Timestamp on first USN record: 2015-10-09 21:37:58.836242

–quick Warning: This logic does make some assumptions abou the data in question and could use more testing. If you are experiencing issues using this functionality just switch back to using usn.py without the –quick flag. I am adjusting its logic every chance I can to make it more helpful/accurate.

Speaking of the USN Journal being a Sparse File - IMO, a major pain point when parsing a USN journal is its size on disk. These files can easily scale over 20GB, comprised of a large amount of leading x00 values. This means the script needs to ‘hunt’ for and find the first USN record before it can begin producing results.

Using an interpreted language such as Perl or Python to do this initial hunting can be extremely time consuming if an Analyst is working with a larger journal file. Applying the –quick / -q flag enables the script to perform this search much more quickly: by jumping ahead a gigabyte at a time looking for data. Jumping ahead one gigabyte at a time requires the journal in question to be at least one gigabyte in size. If it isn’t, the script will simply produce an error and exit:

dev@computer$ python usn.py usnJRNL --quick
[ - ] This USN journal is not large enough for the --quick functionality
[ - ] Exitting...

Below is an example of the time it takes to find valid data in a large USN journal - 39GB in size. This example is not using the –quick functionality and takes over six minutes to even begin parsing data:

PS Dev:\Desktop> Measure-Command {C:\Python27\python.exe usn.py usnJRNL}
Hours             : 0
Minutes           : 6
Seconds           : 3
Milliseconds      : 766
Ticks             : 3637662181
TotalDays         : 0.00421025715393519
TotalHours        : 0.101046171694444
TotalMinutes      : 6.06277030166667
TotalSeconds      : 363.7662181
TotalMilliseconds : 363766.2181

Now the same USN journal file, but with the –quick flag invoked. The time it takes to find data is cut down to just under three seconds:

PS Dev:\Desktop> Measure-Command {C:\Python27\python.exe usn.py usnJRNL --quick}
Hours             : 0
Minutes           : 0
Seconds           : 2
Milliseconds      : 822
Ticks             : 28224455
TotalDays         : 3.2667193287037E-05
TotalHours        : 0.000784012638888889
TotalMinutes      : 0.0470407583333333
TotalSeconds      : 2.8224455
TotalMilliseconds : 2822.4455

–csv

Using the CSV flag will, as expected, provide results in CSV format. For now, using the –csv / -c option will provide:

  • Timestamp
  • Filename
  • File attributes
  • Reason

At this point the –csv flag cannot be combined with any other flag other than –quick. That should change soon, as I want –csv capability for any data returned. An example of what this looks like is below:

dev@computer:~$python usn.py usnJRNL --csv
timestamp,filename,fileattr,reason
2015-10-09 21:37:58.836242,A75BFDE52F3DD8E6.dat,ARCHIVE NOT_CONTENT_INDEXED,DATA_EXTEND FILE_CREATE

–verbose

Returns all USN record properties with each entry, with the –verbose / -v flag. The result is a JSON object.

dev@computer:~$python usn.py usnJRNL --verbose
{
    "recordlen": 88,
    "majversion": 2,
    "minversion": 0,
    "fileref": 281474976767661,
    "pfilerefef": 844424930233360,
    "usn": 419506120,
    "timestamp": "2015-10-09 21:38:52.160484",
    "reason": "CLOSE FILE_DELETE",
    "sourceinfo": 0,
    "sid": 0,
    "fileattr": "ARCHIVE",
    "filenamelen": 24,
    "filenameoffset": 60,
    "filename": "wmiutils.dll"
}

–filename Sometimes during a more targeted investigation, an Analyst is simply looking for additional supporting evidence to confirm what is believed or pile on to what is already known - and does not want to eyeball the entire journal for this evidence. By using the ‘filename’ command-line flag, an Analyst can return only USN records which contain the given string in its ‘filename’ attribute:

dev@computer:~$ python usn.py usnJRNL --filename jernuhl
{
    "recordlen": 88,
    "majversion": 2,
    "minversion": 0,
    "fileref": 5910974510924810,
    "pfilerefef": 1688849860348307,
    "usn": 461014088,
    "timestamp": "2015-10-28 01:59:56.233596",
    "reason": "FILE_CREATE",
    "sourceinfo": 0,
    "sid": 0,
    "fileattr": "ARCHIVE",
    "filenamelen": 22,
    "filenameoffset": 60,
    "filename": "jernuhl.txt"
}

—last In the same vain as the –filename / -f functionality, perhaps the Analyst only wants USN records for a certain range of dates. This is somewhat possible through usn.py - by specifying the last n number of days, the script will return only USN journal records for those days. The command below was executed on 11/3/15 and asks for records starting within the last seven days (including the current date):

dev@computer:~$ python usn.py usnJRNL --last 7
{
    "recordlen": 136,
    "majversion": 2,
    "minversion": 0,
    "fileref": 844424930247194,
    "pfilerefef": 281474976710685,
    "usn": 452708840,
    "timestamp": "2015-10-28 00:46:51.412002",
    "reason": "CLOSE FILE_DELETE",
    "sourceinfo": 0,
    "sid": 0,
    "fileattr": "ARCHIVE",
    "filenamelen": 72,
    "filenameoffset": 60,
    "filename": "$TxfLogContainer00000000000000000003"
}
...
...
...

Python Requirements

  • argparse
  • collections
  • datetime
  • json
  • os
  • struct
  • sys

To-Do

  • Enable –csv / -c to work with all other flags, not just with –quick / -q

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