SEC Consult SA-20170511-0 :: Stack-based buffer overflow vulnerability in Guidance Software EnCase Forensic Imager

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A blog post with additional information is available here:
http://blog.sec-consult.com/2017/05/chainsaw-of-custody-manipulating.html=


We have also released a video showing arbitrary code execution:
https://www.youtube.com/watch?v=3D1EngNIXSNQw


SEC Consult Vulnerability Lab Security Advisory < 20170511-0 >
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              title: Stack based buffer overflow
            product: Guidance Software EnCase Forensic Imager
 vulnerable version: EnCase Forensic Imager <=3D 7.10
      fixed version: -
         CVE number: -
             impact: critical
           homepage: https://www.guidancesoftware.com/encase-forensic-ima=
ger
              found: 2017-02-17
                 by: W. Ettlinger (Office Vienna)
                     SEC Consult Vulnerability Lab

                     An integrated part of SEC Consult
                     Bangkok - Berlin - Linz - Luxembourg - Montreal - Mo=
scow
                     Kuala Lumpur - Singapore - Vienna (HQ) - Vilnius - Z=
urich

                     https://www.sec-consult.com

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Vendor description:
-------------------
"When time is short and you need to acquire entire volumes or selected
individual folders, EnCase Forensic Imager is your tool of choice. Based =
on
trusted, industry-standard EnCase Forensic technology, EnCase Forensic Im=
ager:
* Is free to download and use
* Requires no installation
* Is a standalone product that does not require an EnCase Forensic licens=
e
* Enables acquisition of local drives (network drives are not able to be
  acquired with Imager)
* Provides easy viewing and browsing of potential evidence files, includi=
ng
  folder structures and file metadata
* Can be deployed via USB stick and used to perform acquisition of a live=

  device"

URL: https://www.guidancesoftware.com/encase-forensic-imager


Business recommendation:
------------------------
SEC Consult recommends not to use EnCase Forensic Imager for forensic ana=
lysis
until a thorough security review has been performed by security professio=
nals
and all identified issues have been resolved.


Vulnerability overview/description:
-----------------------------------
EnCase Forensic Imager fails to check the length of strings copied from t=
he
definitions of logical volumes in an LVM2 partition. When EnCase Forensic=
 Imager
is used to analyze a crafted LVM2 partition, part of the stack is overwri=
tten
with attacker controlled data. This allows an attacker to overwrite a poi=
nter
to code. After the program execution is transferred to the address specif=
ied in
this pointer, the attacker has control of the consequent program executio=
n.

SEC Consult was able utilize this vulnerability to craft a disk image tha=
t, when
analyzed, executes arbitrary code. Since EnCase Forensic Imager runs with=

administrative privileges, this code runs in an elevated context.

Since EnCase Forensic Imager does not use ASLR or Control Flow Guard, the=

probability that an attacker can successfully exploit this vulnerability =
(and
possibly other vulnerabilities) is significantly higher than in similar s=
oftware
that utilizes these mechanisms.


Proof of concept:
-----------------
In order to parse the name of a logical volume from a logical volume defi=
nition
EnCase Forensic Imager processes a line that e.g. looks as follows:

testlv {

In order to extract the volume name from this string, EnCase Forensic Ima=
ger
first searches for the character { within the line and then copies all =
data
before into another buffer. Since the source buffer is 1024 UTF-16
characters long and the destination buffer is only 258 UTF-16 characters =
long,
a buffer overflow occurs on the stack.

After a function pointer in the stack frame of the calling method has bee=
n
overwritten, this function pointer is being called. Since the method does=
 not
return between overwriting the stack and calling the function pointer, st=
ack
cookies do not protect against this vulnerability.

A demonstration of an exploit has been developed and provided to the vend=
or.
This exploit creates an LVM2 image that defines a logical volume with a
manipulated name. When the investigator searches for LVM2 logical volumes=
 on
this image the aforementioned pointer on the stack is overwritten. Afterw=
ards,
this pointer is called and execution is transfered to a stack pivot gadge=
t.
Since only strings converted from Windows-1252 to UTF-16 strings can be u=
sed in
the overwritten stack memory and since characters below a are transfor=
med,
a series of ROP-chains was required to exploit this vulnerability.
Ultimately the last ROP chain calls VirtualProtect to allow execution of =
the
attacker-supplied code.

The exploit has been developed to work with the 32-bit version of EnCase
Forensic Imager and will be published at a later date.


Vulnerable / tested versions:
-----------------------------
At least version 7.10 of EnCase Forensic Imager has been found to be vuln=
erable.
This version was the latest at the time the security vulnerabilitiy was
discovered.


Vendor contact timeline:
------------------------
2017-02-17: Vulnerability identified, further internal analysis (special =
thanks
            to R. Freingruber for binary exploitation support)
2017-03-07: Sending encrypted advisory to vendor through previous contact=
 via
            email
2017-03-13: Vendor answer: forwarding advisory to engineers, will update =
us
2017-03-17: Sending Proof of Concept exploit to vendor
2017-03-31: Requesting status update (no response)
2017-04-18: Requesting status update, reminding vendor of upcoming public=

            release of the advisory (no response)
2017-05-01: Informing vendor (through all available contacts) of the set =
release
            date (2017-05-11)
2017-05-03: Informing four members of executive team about the upcomming
            release
2017-05-03: Guidance Software says they will inform us "if and when furth=
er
            information is available"
2017-05-09: Informing CERTs (US-CERT, CERT-Bund, CERT.at) about upcoming =
release
2017-05-11: Public release of the security advisory


Solution:
---------
The vendor did not provide a fixed version of the affected application.


Workaround:
-----------
None


Advisory URL:
-------------
https://www.sec-consult.com/en/Vulnerability-Lab/Advisories.htm


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SEC Consult Vulnerability Lab

SEC Consult
Bangkok - Berlin - Linz - Luxembourg - Montreal - Moscow
Kuala Lumpur - Singapore - Vienna (HQ) - Vilnius - Zurich

About SEC Consult Vulnerability Lab
The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. I=
t
ensures the continued knowledge gain of SEC Consult in the field of netwo=
rk
and application security to stay ahead of the attacker. The SEC Consult
Vulnerability Lab supports high-quality penetration testing and the evalu=
ation
of new offensive and defensive technologies for our customers. Hence our
customers obtain the most current information about vulnerabilities and v=
alid
recommendation about the risk profile of new technologies.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Interested in improving your cyber security with the experts of SEC Consu=
lt?
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m
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mail: research at sec-consult dot com
Web: https://www.sec-consult.com
Blog: http://blog.sec-consult.com
Twitter: https://twitter.com/sec_consult

EOF W. Ettlinger @2017


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