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Multiple Vendor ImageMagick Sign Extension Vulnerability
------------------------------------------------------------------------
SUMMARY
ImageMagick is "a suite of image manipulation tools (animate, composite,
conjure, convert, display, identify, import, mogrify and montage) that are
sometimes used by other applications for processing image files". Remote
exploitation of a sign extension vulnerability in ImageMagick, as included
in various vendors' operating system distributions, allows attackers to
execute arbitrary code.
DETAILS
Vulnerable Systems:
* ImageMagick version 6.3.4
Immune Systems:
* ImageMagick version 6.3.5-9
This vulnerability specifically exists in the ReadDIBImage() as shown
below.
558 image->columns=(unsigned long) dib_info.width
...
620
bytes_per_line=4*((image->columns*dib_info.bits_per_pixel+31)/32);
621 length=bytes_per_line*image->rows;
622 pixels=(unsigned char *) AcquireMagickMemory((size_t) MagickMax(
623
bytes_per_line,image->columns+256)*image->rows*sizeof(*pixels));
...
629 count=ReadBlob(image,length,pixels);
...
638 status=DecodeImage(image,dib_info.compression ? MagickTrue :
MagickFalse,pixels);
At line 558, "dib_info.width" is a signed short, which is extended to an
unsigned long and assigned to "image->columns". For example, a value of
0x8000 will be extended to 0xffff8000. Later, it is used as a multiplier
when calculating the allocation size. An integer overflow occurs, leading
to a heap block of insufficient size being allocated. Consequently, a heap
buffer overflow occurs.
Analysis:
Exploitation of this vulnerability allows an attacker to execute arbitrary
code in the context of the user.
One way of exploiting this vulnerability is to persuade a targeted user to
open a malicious image file with a program that utilizes the ImageMagick
library.
As the tools that are part of ImageMagick are sometimes used as helper
tools by other applications, this user may be the same as the web server
user. This scenario is somewhat more severe than the previously described
attack vector since the image processing can occur automatically.
Workaround:
Exposure to this vulnerability can be mitigated by moving or deleting the
related module files. The file locations may vary between distributions.
The globbing expression listed below corresponds to a Red Hat Linux
system.
/usr/lib/ImageMagick-*/modules*/coders/dib.*
Vendor response:
The ImageMagick maintainers have addressed this vulnerability with the
release of version 6.3.5-9. More information is available from the
following URL.
<http://studio.imagemagick.org/pipermail/magick-announce/2007-September/000037.html>
http://studio.imagemagick.org/pipermail/magick-announce/2007-September/000037.html
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-4988>
CVE-2007-4988
Disclosure Timeline:
09/04/2007 - Initial vendor notification
09/05/2007 - Initial vendor response
09/19/2007 - Public disclosure
ADDITIONAL INFORMATION
The information has been provided by
<mailto:idlabs-advisories@idefense.com> iDefense Labs Security Advisories.
The original article can be found at:
<http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=597>
http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=597
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