Title: Remote Command Injection in Arabic Prawn 0.0.1 Ruby Gem

Author: Larry W. Cashdollar, @_larry0

Download Site: http://rubygems.org/gems/Arabic-Prawn

Date: 12/17/2013

In Arabic-Prawn-0.0.1/lib/string_utf_support.rb, the following lines pass unsanitized input to the shell.

426 var = %x{ /usr/bin/curl -I -L --fail --silent --connect-timeout #{seconds} --max-time #{seconds+10} #{url}; /bin/echo -n $? }.to_i
427

428             #return false unless var == 0
429             raise "Failed to create connection to web site: #{url}  --  curl error code: #{var}  --  " unless var     == 0
430 
431             str = %x{ /usr/bin/curl -L --fail --silent --connect-timeout #{seconds} --max-time #{seconds+10} #{url} | \
432                       /usr/bin/grep -Eo -m 1 \"(charset|encoding)=[\\"']?[^\\"'>]+\" | /usr/bin/grep -Eo \"[^=\\"    '>]+$\" }

443             %x{ /usr/bin/touch #{downloaded_file} 2>/dev/null }
444             raise "No valid HTML download file (path) specified!" unless File.file?(downloaded_file)
445             %x{ /usr/bin/curl -L --fail --silent --connect-timeout #{seconds} --max-time #{seconds+10} -o #{downloaded_file} #{url} }
446 
447             simple_test = %x{ /usr/bin/file -ik #{downloaded_file} }    #  cf. man file

If the downloaded file name #{downloaded_file} or #{url} contains any shell meta characters like ';' a malicious user can inject shell commands.

PoC

myfile;id;.txt

id would be passed to the command line and executed.