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Bot controller mimicry

Published: 2008-07-15
Last Updated: 2008-07-15 23:10:24 UTC
by Maarten Van Horenbeeck (Version: 1)
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For a long time I've advocated the use of security intelligence principles in information security. Often considered merely playful though interesting, increasing our knowledge and understanding of a threat reduces our uncertainty in making a response decision. Using time-tested, validated responses is important, but innovation should not be limited to the offenders only.

Joe Stewart, a researcher at Secureworks, published an interesting piece of research today which is just great afternoon reading. His research of the Coreflood network, a pest for about six years now, has so far covered the "who", "why" and "how" of infection. Today, he is also looking at using the botnet's own command & control channel to remove it from a corporate network.

Whether you favour this type of technique or would discard it out of hand, it definitely makes for a fascinating read.

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BlackBerry PDF parsing vulnerability

Published: 2008-07-15
Last Updated: 2008-07-15 22:39:40 UTC
by Maarten Van Horenbeeck (Version: 1)
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Francois wrote in today pointing us to a vulnerability recently discovered in the BlackBerry attachment service. This service parses documents in various file formats, including PDF, and encodes them in a format readable for the BlackBerry handheld device. Most vulnerabilities that have affected the BlackBerry Enterprise platform have been situated in this service, as it needs to be able to parse a wide number of different files, increasing the risk of software vulnerabilities, particularly heap overflows.

Early 2006, for example, a vulnerability in the service affected the parsing of TIFF files. While it's hardly ever adhered to, many hardening guidelines for BlackBerry, including those issued by Australia's DSD, recommend installing the attachment service on a separate machine within a clean and screened subnet. By only allowing files into the service and the resulting datastream out, the impact of a compromise can be controlled.

This vulnerability is interesting as it is one of those cases where it appears the BlackBerry, which opens a file, may be at risk, but what is really exposed in the enterprise setup housed in the centre of the corporate network. Users of the BlackBerry Enterprise Server (BES) can read up on the risk and countermeasures here.

 

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Oracle (and BEA, Hyperion and TimesTen) critical patch update July 15th, 2008

Published: 2008-07-15
Last Updated: 2008-07-15 20:45:56 UTC
by Maarten Van Horenbeeck (Version: 2)
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Today, July 15th, Oracle has released its quarterly critical patch update. The highest CVSS score of all vulnerabilities patched is 6.8 (6.5 is the maximum for the Oracle Database itself).

Below is the list of software affected, as listed in the pre-release announcement:

    • Oracle Database 11g, version 11.1.0.6
    • Oracle Database 10g Release 2, versions 10.2.0.2, 10.2.0.3, 10.2.0.4
    • Oracle Database 10g, version 10.1.0.5
    • Oracle Database 9i Release 2, versions 9.2.0.8, 9.2.0.8DV
    • Oracle Database 9i, version 9.0.1.5 FIPS+
    • Oracle TimesTen In-Memory Database version 7.0.3.0.0
    • Oracle Application Server 10g Release 3 (10.1.3), versions 10.1.3.1.0, 10.1.3.3.0
    • Oracle Application Server 10g Release 2 (10.1.2), versions 10.1.2.2.0, 10.1.2.3.0
    • Oracle Application Server 10g (9.0.4), version 9.0.4.3
    • Oracle Application Server 9i Release 1, version 1.0.2.2
    • Oracle Hyperion BI Plus versions 9.2.0.3, 9.2.1.0, and 9.3.1.0
    • Oracle Hyperion Performance Suite versions 8.3.2.4, and 8.5.0.3
    • Oracle E-Business Suite Release 12, version 12.0.4
    • Oracle E-Business Suite Release 11i, version 11.5.10.2
    • Oracle Enterprise Manager Database Control 11i version 11.1.0.6
    • Oracle Enterprise Manager Database Control 10g Release 2, versions 10.2.0.2, 10.2.0.3, 10.2.0.4
    • Oracle Enterprise Manager Database Control 10g Release 1, version 10.1.0.5
    • Oracle Enterprise Manager Grid Control 10g Release 1, versions 10.1.0.5, 10.1.0.6
    • Oracle PeopleSoft Enterprise PeopleTools versions 8.48.18, 8.49.12
    • Oracle PeopleSoft Enterprise CRM version 8.9, 9.0
    • Oracle WebLogic Server 10.0 released through MP1
    • Oracle WebLogic Server 9.0, 9.1, 9.2 released through MP3
    • Oracle WebLogic Server 8.1 released through SP6
    • Oracle WebLogic Server 7.0 released through SP7
    • Oracle WebLogic Server 6.1 released through SP7

Oracle notes that this is the first time patches for BEA, Hyperion and TimesTen technology are included in the release. If you are running software from these recently-acquired vendors, please be aware.

It should be noted that the CVSS for application software vulnerabilities such as a database are generally lower, but not necessarily less critical in specific environments. A bug may not give access to the underlying operating system, but in the case of a database we tend to be more worried about the data housed there than other software running on the same system.

We recommend reviewing the pre-release announcement, and subsequent release, closely, and prioritize patching according to your specific environment's requirements.

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Extracting scripts and data from suspect PDF files

Published: 2008-07-15
Last Updated: 2008-07-15 11:53:58 UTC
by Maarten Van Horenbeeck (Version: 1)
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Over the last few weeks we’ve received a small number of inquiries on how to assess potentially malicious PDF files. As with any file format, there are two ways to get started: either use a sandbox running a presumed vulnerable version of the file parser (in this case Acrobat Reader), or to have a closer look at the file format.

The former is really the easiest way to go and is probably suitable for most situations. The vast majority of exploit PDFs we have seen execute reliably on an unpatched Acrobat Reader 7, so it’s trivial to get this going. However, in some cases you may want to know about the execution path inside the PDF, and not purely how it affects a random target system, or you may just not have a sandbox environment handy.

The core document describing the PDF format is the PDF Reference 1.7, which can be downloaded from the Adobe PDF developer center. The most interesting information for analysis purposes - an overview of the format - can be found as of page 90.

Broadly put, PDF files consist of a header indicating the version, followed by a body consisting of several objects. At the end of the file is the so-called xref (or cross-reference) table, which points directly to various objects within the file, to allow speedy access. Updates not only consist of changes to the objects, but also to the xref table.

Simple objects can look like:

5 0 obj
   [statements]
endobj

Such objects generally describe aspects of how the PDF file should be presented. Another type of object is the “stream”, which can contain types of data, such as images or scripts, encoded in a number of different ways.

Just last week, we received a copy of a malicious file “basketball roster.pdf”. Flat file scanning using Virustotal showed that detection of this file was lacking:

basketball_roster.pdf
MD5 44cf41479559b0dc72a2330a9e8ec6c1

AhnLab-V3 2008.7.11.0 2008.07.10 -
AntiVir 7.8.0.64 2008.07.11 HTML/Shellcode.Gen
Authentium 5.1.0.4 2008.07.10 -
Avast 4.8.1195.0 2008.07.11 -
AVG 7.5.0.516 2008.07.11 -
BitDefender 7.2 2008.07.11 -
CAT-QuickHeal 9.50 2008.07.10 -
ClamAV 0.93.1 2008.07.11 -
DrWeb 4.44.0.09170 2008.07.11 -
eSafe 7.0.17.0 2008.07.10 -
eTrust-Vet 31.6.5946 2008.07.11 -
Ewido 4.0 2008.07.11 Not-A-Virus.Exploit.Win32.Pidief.ax
F-Prot 4.4.4.56 2008.07.10 -
F-Secure 7.60.13501.0 2008.07.10 -
Fortinet 3.14.0.0 2008.07.11 -
GData 2.0.7306.1023 2008.07.11 -
Ikarus T3.1.1.26.0 2008.07.11 HTML.Shellcode
Kaspersky 7.0.0.125 2008.07.11 -
McAfee 5336 2008.07.10 -
Microsoft 1.3704 2008.07.11 -
NOD32v2 3262 2008.07.11 -
Norman 5.80.02 2008.07.10 -
Panda 9.0.0.4 2008.07.10 -
Prevx1 V2 2008.07.11 -
Rising 20.52.41.00 2008.07.11 -
Sophos 4.31.0 2008.07.11 -
Sunbelt 3.1.1509.1 2008.07.04 -
Symantec 10 2008.07.11 -
TheHacker 6.2.96.376 2008.07.10 -
TrendMicro 8.700.0.1004 2008.07.11 -
VBA32 3.12.6.9 2008.07.11 -
VirusBuster 4.5.11.0 2008.07.10 -
Webwasher-Gateway 6.6.2 2008.07.11 Script.Shellcode.Gen

The first thing I generally do with this type of file is to look for any embedded Javascript. Most bugs affecting Acrobat Reader have involved the Javascript method handling engine, so this is a likely first jump. A quick search for interesting objects with a hex editor revealed two interesting ones: one Javascript, the other containing a binary:

The stream description indicates that a filter FlateDecode has been applied to the bitstream. The PDF standard supports 10 different binary filters, of which FlateDecode is the most common. The reader applications use zlib’s deflate to unpack compressed data, which both allows a wider set of characters to be used, as well as makes the overall file smaller than the sum of its uncompressed objects.

In this case, as both suspicious objects are have been rendered unreadable through compression, we want to uncompress them for further review. The easiest command-line way to inflate deflated PDF content is by using the pdfinflt.ps script included with Ghostscript:

[maarten@mojave ghostscript-8.54]$ gs -- toolbin/pdfinflt.ps /tmp/roster.pdf /tmp/roster.out

ESP Ghostscript 815.02 (2006-04-19)
Copyright (C) 2004 artofcode LLC, Benicia, CA.  All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
   **** Warning: File has a corrupted %%EOF marker, or garbage after %%EOF.
   **** Warning:  An error occurred while reading an XREF table.
   **** The file has been damaged.  This may have been caused
   **** by a problem while converting or transfering the file.
   **** Ghostscript will attempt to recover the data.
   **** Warning:  There are objects with matching object and generation
   **** numbers.  The accuracy of the resulting image is unknown.
ERROR: /undefined in /BXlevel
Operand stack:
   --nostringval--   51   0   2   --dict:6/6(ro)(G)--   obj
Execution stack:
   %interp_exit   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push   1   3   %oparray_pop   1   3   %oparray_pop   1   3   %oparray_pop   1   3   %oparray_pop   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push   --nostringval--   %loop_continue   --nostringval--
Dictionary stack:
   --dict:1087/1686(ro)(G)--   --dict:0/20(G)--   --dict:143/200(L)--   --dict:241/347(ro)(G)--   --dict:18/24(L)--
Current allocation mode is local
Current file position is 4774
ESP Ghostscript 815.02: Unrecoverable error, exit code 1

[maarten@mojave ghostscript-8.54]$

Alas, in many cases, PDF exploits are not created using the most standards-compliant generators, and in the case where they exploit a parser issue, well, it makes sense that they don’t parse cleanly. Inflating all objects in the file using a stock tool seems to be a no-go.

Luckily, there’s a great version of the zlib libraries for Perl, and it’s trivial to write an inflater script:

use Compress::Zlib ;
$processor = inflateInit();

binmode STDIN;
binmode STDOUT;

while (read(STDIN, $flatfish, 8192))
{
 $blowfish = $processor->inflate($flatfish) ;
 print $blowfish
}

die "Parsing error or end of stream\n"


The only thing remaining now would be to copy-paste the stream content from the file into a new binary file, and feed it into the script. However, things get a little bit more complicated. While the deflated content is zlib, PDF uses a slightly different zlib header structure than what the libraries expect.

When opening the PDF in a hex editor, the stream actually starts after the 0D 0A marker following the “stream” string. The next two bytes, 48 89, are in fact the PDF header. In order to make the stream compatible with zlib, change these into a header acceptable to zlib, such as 78 9C. Next, run this file through the Perl script again, with much better results:

[maarten@mojave ~]$ perl inflate.pl < /tmp/deflated.txt
function re(count,what)
{
var v = "";
while (--count >= 0)
v += what;
return v;
}
function start()
{
sc = unescape("%uc933%ub966%u018c%u1beb%u565e%ufe8b%u66ac%u612d%u6600%ue...

}
if (app.viewerVersion >= 6.0)
{
this.collabStore = Collab.collectEmailInfo({subj: "",msg: plin});
}
}


From there, you can apply regular Javascript deobfuscation techniques, as discussed in previous diary entries, to investigate the actual scripting employed. In this specific case, the script creates a crafted set of data which exploits a known vulnerability in the Collab.collectEmailInfo function of Acrobat Reader’s Javascript engine (CVE-2007-5659).

-- Maarten

Keywords: PDF malware zlib
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