Date: Sun, 29 May 2016 15:03:10 -0500 (CDT) From: Bob Friesenhahn <bfriesen@...ple.dallas.tx.us> To: oss security list <oss-security@...ts.openwall.com> Subject: CVE Request: GraphicsMagick and ImageMagick popen() shell vulnerability via filename All existing releases of GraphicsMagick and ImageMagick support a file open syntax where if the first character of the file specification is a '|', then the remainder of the filename is passed to the shell for execution using the POSIX popen(3C) function. File opening is handled by an OpenBlob() function in the source file blob.c. Unlike the vulnerability described by CVE-2016-3714, this functionality is supported by the core file opening function rather than a delegates subsystem usually used to execute external programs. The funtionality can be demonstrated as follows: % rm -f hello.txt % convert '|echo Hello > hello.txt;' null: % ls hello.txt hello.txt The same weakness in the native SVG readers may be used to provoke this problem. This example returns a valid image given a known file (but an actual file is not necessary): <?xml version="1.0" standalone="no"?> <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"> <svg width="4in" height="3in" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"> <desc>Illustrates how a shell command may be embedded in a SVG. </desc> <image x="200" y="200" width="100px" height="100px" xlink:href="|echo Hello > hello.txt; cat /usr/lib/firefox/browser/icons/mozicon128.png"> <title>My image</title> </image> </svg> Or in MVG: push graphic-context viewbox 0 0 640 480 image copy 200,200 100,100 "|echo Hello > hello.txt; cat /usr/lib/firefox/browser/icons/mozicon128.png" pop graphic-context Previously supplied recommended patches for GraphicsMagick do successfully block this attack vector in SVG and MVG. It is highly likely that there are many paths leading to a suitable filename which may be executed outside of SVG and MVG since the software is quite complex and powerful. The examples above are not meant to suggest that other avenues to the same weakness are not available. The simple solution to the problem is to disable the popen support (HAVE_POPEN) in GraphicsMagick's magick/blob.c as is done by the attached patch. This issue was discovered by Bob Friesenhahn, of the GraphicsMagick project. Bob -- Bob Friesenhahn bfriesen@...ple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ diff -r 33200fc645f6 magick/blob.c --- a/magick/blob.c Sat Nov 07 14:49:16 2015 -0600 +++ b/magick/blob.c Sun May 29 14:12:57 2016 -0500 @@ -68,6 +68,7 @@ */ #define DefaultBlobQuantum 65541 +#undef HAVE_POPEN /* Enum declarations.
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