iDefense Security Advisory 09.19.07: Multiple Vendor ImageMagick Off-By-One Vulnerability

Multiple Vendor ImageMagick Off-By-One Vulnerability

iDefense Security Advisory 09.19.07
Sep 19, 2007


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.
For more information about ImageMagick, visit the vendor's site at the
following URL.


Remote exploitation of an off-by-one vulnerability in ImageMagick, as
included in various vendors' operating system distributions, allows
attackers to execute arbitrary code.

This vulnerability specifically exists in the ReadBlobString() function
in magick/blob.c as shown below.

3110 for (i=0; i < (long) MaxTextExtent; i++)
3111 {
3112 p=ReadBlobStream(image,1,buffer,&count);
3119 string[i]=(char) (*p);
3120 if ((string[i] == '\n') || (string[i] == '\r'))
3121 break;
3122 }
3123 string[i]='\0';

The variable "string" is a character array of length "MaxTextExtent". An
off-by-one buffer overflow will occur on line 3123 when "i" is exactly
"MaxTextExtent". This function is called from several image file
processing routines. Most of the buffers involved are stack based,
although some are on the heap.


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

Exploitation in stack-based scenarios depends on the stack layout, which
depends on the compiler and compiler options used to build the library.


iDefense Labs confirmed that ImageMagick version 6.3.4 is vulnerable. It
is suspected that other versions of ImageMagick are also vulnerable.


iDefense is unaware of any effective workaround for this vulnerability.


The ImageMagick maintainers have addressed this vulnerability with the
release of version 6.3.5-9. More information is available from the
following URL.


The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-4987 to this issue. This is a candidate for inclusion in
the CVE list (, which standardizes names for
security problems.


09/04/2007 Initial vendor notification
09/05/2007 Initial vendor response
09/19/2007 Coordinated public disclosure


This vulnerability was reported to iDefense by regenrecht.

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Copyright © 2007 iDefense, Inc.

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