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forensic-timelines

VIEWS: 24 PAGES: 53

									                           Forensic Timelines
                                 Steve Romig
                                 October, 2011




Sunday, October 23, 2011
                                              Agenda



                    •      What is a Forensics Timeline? Why should you be interested
                           in them?

                    •      How do you make them?

                    •      Some examples.

                    •      A few important considerations.




Sunday, October 23, 2011
                             What, Why is a
                           Forensics Timeline?



Sunday, October 23, 2011
                                  What/Why are they?
                    •      A forensics timeline is a portrayal of chronological activity
                           gleaned from evidence pertaining to a forensic computer
                           investigation.

                    •      Much of what we do in forensics investigations revolves
                           around reconstructing past sequences of events.

                    •      We could include any sort of evidence that can be linked to
                           a specific time or to a range of times.

                    •      It is *very* helpful to “cast a wide net” as we construct our
                           timelines - this gives us a broader view of what happened
                           and can give surprising insights.

                    •      In the last few years this technique of merging time-based
                           evidence from multiple sources has been given a name
                           (“super timelines”) and some useful tools have been written
                           to help create and manage them.

Sunday, October 23, 2011
                           How do you make
                                them?



Sunday, October 23, 2011
                             How do you make them?


                    •      Step one: gather some time-based evidence

                    •      Step two: convert it to some common format and mush it
                           together

                    •      Step three: visualization

                    •      Step four: pour through it, understand it, interpret it,
                           annotate it, draw conclusions, look for more evidence, goto
                           step two, three or four and repeat




Sunday, October 23, 2011
                           Gather Evidence



Sunday, October 23, 2011
                                       Gather Evidence

                    •      Any time-based evidence is fair game. The usual suspects
                           include: file system timestamps (so-called MAC times), logs
                           with timestamped entries (such as Unix “wtmpx”, netflow
                           logs, syslog, event log, etc.), the “recycler” folder, timestamps
                           within archives.

                    •      Check with your network folks to see what they might have:
                           netflow, firewall, IDS, authentication, DHCP, router or cable
                           modem logs...

                    •      Logs from any external service providers that might be of
                           interest (email servers, web sites such as blogs, Facebook,
                           Twitter, the phone/cable company, your ISP...)




Sunday, October 23, 2011
                                       Gather Evidence
                    •      Not so obvious sources:

                           •   Registry folder modification times.

                           •   Process start times (from “ps” listing or process
                               accounting records), end times (from process accounting).

                           •   Some Unix shell history files (if so configured).

                           •   Scheduled tasks, Cron entries, etc: compare against the
                               logs of this activity (anything missing that ran but didn’t
                               get logged, or didn’t run?)

                           •   Email (logs as well as messages).

                           •   Browser artifacts - history, cookies, bookmarks...

                           •   Packet captures from Tcpdump, Wireshark or equiv.


Sunday, October 23, 2011
                                       Gather Evidence
                    •      More not so obvious sources:

                           •   Anti-virus, anti-spyware logs: from the local machine, from
                               central servers.

                           •   Logs from Dr. Watson, Malware Bytes, HiJack This!,
                               Windows Defender...

                           •   EXIF data from pictures.

                           •   PE headers from binaries carry the compile time.

                           •   Chat logs.

                           •   Restore points, especially from the registry snapshots.

                           •   Mobile phones: calls, SMS...

                           •   Calendars!

Sunday, October 23, 2011
                                 How to Get the Data?
                    •      Use EnCase (or some similar forensics application)

                           •   Export file system entries as CSV (all fields). I find it
                               useful to do this once for everything, then again for all
                               “malware”, then for registries (pick “view file structure”
                               and filter for registry keys and export those). This allows
                               you to tag each in different ways in your data (and to
                               colorize them if you so choose).

                           •   Search for Internet History, and then export the resulting
                               records as CSV (again, all fields). This can result in a
                               tremendous amount of data...

                           •   Search for email, export...

                           •   Parse Event Logs and export the associated bookmarks.

                           •   Find interesting log files, “copy/unerase” them.

Sunday, October 23, 2011
                                 How to Get the Data?



                    •      Use Sleuthkit (or something similar, like SIFT)

                           •   e.g. “fls -m ‘C:/’ -f ntfs -r foo.dd > bodyfile”

                           •   mactime -d -b bodyfile > csvfile

                    •      Use timescanner (part of Kristinn Gudjonsson’s log2timeline
                           project, more on this below)




Sunday, October 23, 2011
                     Convert to a Common
                      Format and Merge



Sunday, October 23, 2011
                                            Perl/Python
                    •      If you know Perl, Python or some other language suitable for
                           string manipulation, its easy to cobble together scripts that
                           read data in different formats and convert it to a common
                           format.

                    •      I’ve being doing this with Perl for years, and have scripts that
                           read EnCase exports (file times, internet history, event log),
                           netflow, bro, McAfee EPO, McAfee OnAccess scan logs,
                           UNIX wtmp logs, and others.

                    •      If you go this route I suggest that you convert everything to
                           CSV or TSV format, and use a common schema for the first
                           few columns: date, time, host, type of entry (file, internet, ids
                           log...), type of access (access, write, browse, ids alert, info
                           msg...) Trying to convert *all fields* of *everything* into a
                           common schema is difficult.


Sunday, October 23, 2011
                             log2timeline, timescanner


                    •      But my scripts are goofy, and why go to the trouble when
                           there’s a better alternative. Kristinn Gudjonsson wrote
                           log2timeline to convert dozens of time-based data to
                           common formats (plural).

                    •      Reads: data from web servers, browsers, mactime body files,
                           McAfee, generic Unix logs, EnCase and FTK directory
                           listings, eventlog, pcap, metadata from EXIF, PDF, etc...

                    •      Writes: CEF, CSV, Simile, TSV/TLN, etc.




Sunday, October 23, 2011
                                          TimeScanner



                    •      Timescanner is a front-end to log2timeline. It reads a
                           directory tree looking for files that log2timeline can parse,
                           parses them, and exports the results.

                           •   Typical use would be to mount your evidence image as a
                               read-only filesystem(s) and then run timescanner against
                               them.




Sunday, October 23, 2011
                           Visualization



Sunday, October 23, 2011
                                 EnCase Timeline View




                    •      I have a love/hate relationship with EnCase. The timeline
                           viewer is one of the parts that I hate. In fact, I loath it.

                    •      I’m sure there are people who find it useful.




Sunday, October 23, 2011
                                         Simile Timeline



                    •      The SIMILE project at MIT has developed a tool for
                           visualizing time-based events called “Timeline”

                    •      I’ve used this a little for visualizing events relating to
                           computer security incidents.

                    •      See http://simile.mit.edu/timeline/




Sunday, October 23, 2011
Sunday, October 23, 2011
Sunday, October 23, 2011
Sunday, October 23, 2011
                                               Zeitline



                    •      Cool visualization aid from Florian Buchholz of CERIAS.

                    •      Allows you to import data from one or more sources,
                           “collate” it, view it, filter...

                    •      Main claim to fame: ability to group events together.




Sunday, October 23, 2011
Sunday, October 23, 2011
Sunday, October 23, 2011
                                             Use Splunk!

                    •      Splunk is particularly well-suited to accepting time-based
                           “stuff” and making it easier for you to make sense out of it.

                    •      The fact that it does “normalization” at search time makes it
                           flexible in the face of unknown input formats.

                    •      You can define fields “on the fly” and apply them at search
                           time, and then use these for correlation, pivoting, etc.

                    •      Extremely powerful and extensible search mechanism. You
                           can add your own perl/python extensions, and/or conduct a
                           search through the CLI and pipe that into a script.

                    •      Splunk rocks...



Sunday, October 23, 2011
                               Never Underestimate...




                    •      Unix command line tools (sed, awk, grep and friends), Perl/
                           Python/Ruby scripts, and emacs!

                    •      Spreadsheets!




Sunday, October 23, 2011
                           Figure it Out



Sunday, October 23, 2011
                                    Insert Comments



                    •      I find it helpful to insert comments (annotated somehow for
                           filtering, possibly color-coded) as I figure things out.

                    •      When you are done you can pull out the comments and get
                           a nice chronological summary of events.




Sunday, October 23, 2011
                               A Simple Example
        (Comments are marked with +++++)

        2006-12-11 08:28:35 host1 fsys access inetinfo.exe
        2006-12-11 08:28:35 host1 fsys access mmsm.exe
        2006-12-11 08:28:35 host1 fsys access netman.dll
        ...
        2006-12-11 08:28:36 host1 registry Folder all\host1_ld0\C\WINDOWS\system32\config\system
            \NTRegistry\$$$PROTO.HIV\ControlSet001\Enum\Root\LEGACY_SRV\0000
        2006-12-11 08:28:36 host1 registry Folder all\host1_ld0\C\WINDOWS\system32\config\system
            \NTRegistry\$$$PROTO.HIV\ControlSet001\Services\lanmanserver\parameters
        2006-12-11 08:28:36 host1 registry Folder all\host1_ld0\C\WINDOWS\system32\config\system
            \NTRegistry\$$$PROTO.HIV\ControlSet002\Enum\Root\LEGACY_SRV\0000
        ...
        2006-12-11 08:28:37 host1 fsys access dcrs.exe
        2006-12-11 08:28:37 host1 fsys access dssenh.dll
        2006-12-11 08:28:37 host1 fsys modify DCRSSDRV.SYS - hacker-defender -----
        2006-12-11 08:28:37 host1 fsys write DCRSSDRV.SYS - hacker-defender -----
        2006-12-11 08:28:37 host1 ----- +++++ bad things happening here!




Sunday, October 23, 2011
                                     Just the Comments...
                           2006-12-10 05:36:37 host1 ----- +++++ install drftpd, done at 5:47, system.exe
                           2006-12-10 07:09:45 host1 ----- +++++ drftp config modified
                           2006-12-10 09:17:34 host1 ----- +++++ drftp connects to 1.2.3.4:64998?
                           2006-12-10 09:26:56 host1 ----- +++++ minwinagent exploit from 4.3.2.1
                           2006-12-11 08:28:37 host2 ----- +++++ bad stuff here
                           2006-12-11 09:25:03 host1 ----- +++++ drftpd people are shutting down?
                           2006-12-11 09:26:05 host1 ----- +++++ minwinagent exploit?
                           2006-12-11 09:26:06 host1 ----- +++++ ping run, h-d modified
                           2006-12-11 09:32:37 host1 ----- +++++ more h-d changes
                           2006-12-11 09:38:13 host1 ----- +++++ drftpd changes
                           2006-12-11 10:14:09 host1 ----- +++++ system.exe run, modified soon
                           2006-12-11 12:10:55 host2 ----- +++++ serv-u config modified
                           2006-12-11 14:21:48 host1 ----- +++++ winlogon.exe fault
                           2006-12-11 14:23:01 host1 ----- +++++ winlogon.exe fault
                           2006-12-11 14:23:02 host1 ----- +++++ mcshield.exe fault
                           2006-12-11 14:23:15 host1 ----- +++++ winlogon.exe fault
                           2006-12-11 14:26:30 host1 ----- +++++ mcshield.exe fault
                           2006-12-11 14:26:36 host1 ----- +++++ mcshield.exe fault




Sunday, October 23, 2011
                              Thrashing, er, Searching...


                    •      Say you’re investigating a compromised system. You’re trying
                           to determine when and how the system was compromised,
                           and whether it contains sensitive data and if so, whether that
                           data shows signs of having been accessed.

                    •      You might mount the disk image and do a search for
                           malware with a variety of tools, or search for sensitive data
                           with Identity Finder or some other DLP product. You can
                           tag these in some way (e.g. export as a separate CSV so you
                           can add a text field, or import them into a spreadsheet and
                           color them someway).




Sunday, October 23, 2011
                                              Searching


                    •      Assemble your timeline, including the specially tagged items.
                           Search for these tagged items in your timeline. These might
                           be comment-worthy in their own right, but you should also
                           look at events that are chronologically “near” these - these
                           might be signs of related activity (such as file system activity
                           for files that weren’t detected by your anti-malware scans).

                    •      You’ll want to look at the timestamps for all of the “events of
                           interest” and see whether there’s nearby associated activity
                           (other files, registry entries, log entries that look interesting).




Sunday, October 23, 2011
                                            Searching...



                    •      Activity in your timeline can be fast and furious or spread
                           over time.

                    •      Some malware waits for minutes or even hours before
                           taking action.

                    •      This can make it hard to identify “interesting activity” in a sea
                           of events.




Sunday, October 23, 2011
                                     Spreadsheet Magic
                    •      Searching

                    •      Filtering - show me only X, don’t show me Y

                           •   You can also do magic with grep, awk, sed etc. on the data
                               before importing it into your spreadsheet...

                    •      Colorizing - based on content

                           •   I like to colorize based on the “type” of entry (file system
                               data, internet history, IDS logs...).

                           •   I use light colors for “normal” activity and bright colors
                               for “hey, look here” activity.

                           •   I try to be consistent across investigations: Internet
                               history events are yellow, IDS logs are red, comments are
                               blue (sounds like the start of a bad poem...).

Sunday, October 23, 2011
Sunday, October 23, 2011
Sunday, October 23, 2011
Sunday, October 23, 2011
Sunday, October 23, 2011
Sunday, October 23, 2011
                                     Login Spreadsheet


                    •      In some investigations we have looked at login sessions from
                           different sources: netflow, sshd (via syslog), wtmp and so on.

                    •      Making sense out of this can be confusing. The linear
                           timeline doesn’t help - sessions are overlapping, and there’s
                           too much data.

                    •      Simile timeline could be very useful here (and we’ve used it
                           for this sort of thing, pity I don’t have an example handy... :-)

                    •      Spreadsheets to the rescue again!




Sunday, October 23, 2011
Sunday, October 23, 2011
                                    Login Spreadsheet


                    •      So now we have a list of sessions. We can see that our data
                           sources aren’t as complete as we’d like them to be - some
                           netflow data is missing, some syslog data was dropped (UDP
                           transport isn’t reliable), and some of the wtmp log entries
                           were zero’d out. But correlating them together gives us a
                           reasonably complete picture of everything.

                    •      It would be nice to “filter” the event timeline be login
                           session to get just the events that occurred “within” each
                           session. Easy enough with the appropriate Perl script...




Sunday, October 23, 2011
                                  Time Period Filtering
                    •      So, you’ve got a ton of data with overlapping login sessions
                           for multiple people. How do you make sense of it all?

                    •      One answer:

                           •   Make a list of sessions (defined by a start and end time,
                               typically drawn from TCP sessions from netflow logs, login
                               sessions from authentication logs, etc.)

                           •   Write a script which reads these sessions and pulls out
                               the event activity that falls “within” each session and
                               writes these to a separate output files.

                           •   Read the output files one by one to get a clearer picture
                               of what *might* have been related to activity in that
                               session.

                    •      *NOTE* see “A Few Important Considerations”, next!!

Sunday, October 23, 2011
Sunday, October 23, 2011
Sunday, October 23, 2011
                           A few important
                           considerations.



Sunday, October 23, 2011
                                        Considerations
                    •      There are a few important things to keep in mind when you
                           are assembling or interpreting timelines.

                    •      Take all your evidence with an appropriately large grain of
                           salt.

                           •   Evidence could have been altered to change or destroy
                               “history”. For example: malware that changes its
                               timestamps to match system files, intruders who modify
                               system logs to remove entries.

                           •   Some timestamps (such as file system timestamps) only
                               show the most recent activity: past activity has been
                               obscured.

                           •   Some timestamps (file system access times, especially) are
                               not always updated.


Sunday, October 23, 2011
                                        Considerations

                    •      If you are merging data from multiple sources, beware of
                           time synchronization issues.

                           •   It is prudent to ensure that all of your computers, logging
                               devices, firewalls, etc. synchronize their clocks to common
                               reference (e.g. using NTP) *before* you need to conduct
                               an investigation.

                           •   If possible, confirm that events gathered from different
                               systems appear to have “sane” timestamps. For instance,
                               compare the time that a router recorded the creation of
                               an “ssh” connection to the time that the server logged
                               the connection.




Sunday, October 23, 2011
                                        Considerations
                    •      To correctly interpret the events in your timeline, you need
                           to understand what the events mean. That probably seems
                           obvious.

                           •   A login session involving the ‘romig’ account means that
                               someone using that account logged in, *not* necessarily
                               that the account owner logged in.

                           •   A DHCP lease means that a client with MAC address
                               00:DE:AD:BE:EF:00 was assigned IP address 1.2.3.4, *not*
                               that it was the only computer that *could* have been
                               using that IP address.

                    •      Beware time zone issues.

                           •   Some logs are in local time, some are in UTC. If you are
                               gathering events from multiple systems, are they all in the
                               same timezone?

Sunday, October 23, 2011
                                        Considerations
                    •      Correlating events together can be tricky.

                           •   One problem is event lag. Consider a ssh login session:
                               our Cisco router will generate a netflow record that
                               shows the time the first packet in the TCP connection
                               was seen. The login record for the person who logged in
                               won’t be created until they correctly authenticate, which
                               could be seconds or even minutes later.

                           •   Events that happen at roughly the same time may or may
                               not have anything to do with each other. For instance, if
                               there are 10 people logged into a multi-user system, it
                               would be difficult to tie file system activity back to a
                               specific person based solely on timestamps. Network
                               activity stemming from the computer might have been
                               triggered by one of these people, or by something left
                               running on the system by a previous user.

Sunday, October 23, 2011
                           References



Sunday, October 23, 2011
                                            References


                    •      log2timeline, timescanner (by Kristinn Gudjonsson,
                           kristinn@log2timeline.net): http://log2timeline.net/

                    •      Zeitline (by Florian Buchholz, florian@cerias.purdue.edu):
                           http://projects.cerias.purdue.edu/forensics/timeline.php

                    •      Simile Timeline: http://www.simile-widgets.org/timeline/

                    •      SleuthKit: http://www.sleuthkit.org

                    •      SANS SIFT: http://computer-forensics.sans.org/community/
                           downloads




Sunday, October 23, 2011

								
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