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SEC Consult SA-20161128-0 :: DoS & heap-based buffer overflow in Guidance Software EnCase Forensic

SEC Consult Vulnerability Lab Security Advisory < 20161128-0 >
              title: Denial of service & heap-based buffer overflow
            product: Guidance Software EnCase Forensic Imager & EnCase Forensic
 vulnerable version: EnCase Forensic Imager<= 7.10
                     EnCase Forensic (tested with version
      fixed version: -
         CVE number: -
             impact: high
           homepage: https://www.guidancesoftware.com/encase-forensic-imager
              found: 2016-09-30
                 by: Wolfgang Ettlinger (Office Vienna)
                     SEC Consult Vulnerability Lab

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



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 Imager:
* Is free to download and use
* Requires no installation
* Is a standalone product that does not require an EnCase Forensic license
* Enables acquisition of local drives (network drives are not able to be
  acquired with Imager)
* Provides easy viewing and browsing of potential evidence files, including
  folder structures and file metadata
* Can be deployed via USB stick and used to perform acquisition of a live

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

Business recommendation:
SEC Consult recommends not to use Encase Forensic Imager or the Encase Forensic
Suite until a thorough security review has been performed by security
professionals and all identified issues have been resolved.

Vulnerability overview/description:
1) Denial of Service
Several manipulated hard disk images cause Encase Forensic Imager to crash. A
suspect manipulating the hard drive could potentially hinder an investigator
from using Encase Forensic Imager for creating hard disk images.
Encase Forensic (v7) has been tested and found to be affected as well.

2) Heap-based buffer overflow
Using a manipulated ReiserFS image an attacker can overwrite heap memory on the
investigator's machine. Because of several restrictions SEC Consult was unable
to create an exploit that works reliably within a reasonable timeframe.
However, as with most heap-based buffer overflow vulnerabilities it is possible
that an attacker could gain arbitrary code execution nevertheless.

Proof of concept:
SEC Consult has created proof of concept disk images that will crash Encase. Those
PoC images will not be released.

 1) Denial of Service
The following list demonstrates cases that cause Encase to crash. The
investigators would be unable to analyze the hard disk/partition/image using the
affected products:
 * Ext3:
  - Several conditions cause Encase Forensic Imager to encounter an div/0
    exception. Disk images that were manipulated in the following way
    demonstrate this issue. Those crashes have not been further
    investigated as to whether code execution is possible.
   + nummer of blocks per group: 0xFFFFFFFF
   + total numer of blocks: 0xFFFFFFFF
   + last mount path: 'A'*100000
   + volume name: 'A'*100000
   + block number of the superblock: 0
   + FS-Id: 'A'*100000
  - Manipulating the size of the inode structure value (e.g. 0xFFFF) causes
    Encase Forensic Imager to write beyond the limits of a previously
	allocated (VirtualAlloc) segment.
 * Iso9660:
  - If the length of a file name is specified in a way that it would exceed
    the end of the last block, Encase Forensic Imager crashes while trying to
    read beyond an allocated segment.
 * ReiserFs:
  - When setting a block size of below 0x200 the application overwrites heap
    memory with attacker-supplied data.
 * GPT:
  - When specifying an overly long name (in our setup longer than 0x3fc6) for a
    partition, Encase Forensic crashes failing to read memory when trying to
    determine the length of the string. The partition table can be constructed
    in a way that it can also be used for storing data. However, an investigator
    using Encase will not be able to analyze it.

2) Heap-based buffer overflow
The manipulated ReiserFs image that causes the application to overwrite heap
memory can be tuned to overwrite heap-data with attacker-controlled data.

The application calculates a value (here called "dev_block_count") as:

dev_block_count =
   blocksize from image (e.g. 0x200)
 / blocksize of reading device (typically 0x200)
 * number of blocks

.text:006F5306 mov     ecx, [esi+14Ch] ; ecx = blocksize (device, 0x200)
.text:006F530C movzx   eax, [esp+90h+var_54] ; eax = blocksize (img)
.text:006F5311 xor     edx, edx
.text:006F5313 div     ecx ; div eax / ecx
.text:006F5315 push    0
.text:006F5317 mov     edx, eax
.text:006F5319 imul    edx, [esp+94h+var_80] ; * numblocks

If this value is zero (which is the case when the blocksize from the image is
smaller than 0x200), later in the program it is corrected to the value 1

This causes the application to later allocate 4 bytes of memory (the corrected
value of 1 * 4, @006F5426).

Then the first block of the image is copied to the allocated 4-byte heap space.
The length to be copied is calculated based on the number of blocks specified
in the image (maximum 0x200).

Vulnerable / tested versions:
At least version 7.10 of Encase Forensic Imager has been found to be vulnerable.
This version was the latest at the time the security vulnerabilities were

The disk images that caused crashes for Encase Forensic Imager also caused
crashes with Encase Forensic version It is unknown whether
Encase Forensic v8 is affected as well.

Vendor contact timeline:
2016-10-07: Contacting vendor (sales team) through email, requesting security
            contact, sending responsible disclosure policy & encryption keys
2016-10-14: No answer, extending email recipient list, requesting security
            contact again
2016-10-14: Vendor: our request has been sent to management team, they will
            follow up
2016-10-17: Vendor: one of their security representatives will be reaching
            out shortly.
2016-10-28: Asking again for security contact, kind reminder of latest release
            date per 2016-11-26
2016-10-28: Vendor: Verified that request has been passed on to proper
            department, they will follow up on this
2016-11-07: Asking again for security contact, reminding them again that
            release date is in about three weeks
2016-11-08: Extending email recipient list again, including SVP Product
            Engineering explaining unsuccessful attempts to receive a
            security contact
2016-11-14: Still no answer, reminding Guidance Software again about the release
            date which has been set to 2016-11-28 now. Told them that the
            initial vulnerabilities also affect Encase Forensic and not only
            Encase Forensic Imager.
2016-11-14: Vendor: "send the alleged vulnerability to us for review" (signed
2016-11-14: Sending the advisory encrypted to the vendor, including proof of
            concept disk images to reproduce the issues
2016-11-14: Vendor: "We will look at the issues and will address them in future
            release(s) if necessary"
2016-11-15: Asking if there is a hotfix planned, offering to delay the advisory
            release for a few days if necessary, otherwise we'll keep the set
            release date
2016-11-15: Vendor: they will fix the issue later and are fine patching it after
            advisory release
2016-11-25: Asking if any fixes are available
2016-11-28: Releasing security advisory

The vendor told SEC Consult they investigate the issues and will fix them at a
later date.


Advisory URL:


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. It
ensures the continued knowledge gain of SEC Consult in the field of network
and application security to stay ahead of the attacker. The SEC Consult
Vulnerability Lab supports high-quality penetration testing and the evaluation
of new offensive and defensive technologies for our customers. Hence our
customers obtain the most current information about vulnerabilities and valid
recommendation about the risk profile of new technologies.

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Mail: research at sec-consult dot com
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EOF W. Ettlinger / @2016

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