When Google isn't Google

Published: 2013-06-10
Last Updated: 2013-06-10 12:22:43 UTC
by Johannes Ullrich (Version: 1)
1 comment(s)

Like many other exploit scripts, the recent "Plesk" exploit used a fake user agent of "Googlebot". Attackers assume that most web applications are happy to be indexed by Google and possibly ably no or less stringent filters. For example, some applications will show more content to Google that is not readily displayed to normal users unless these users sign up, solve a captcha or even pay.

Google however makes it pretty easy to distinguish "real" Google bots from fake once. The IP address used by Google will reverse resolve to crawl-a-b-c-d.googlebot.com, where a-b-c-d is the IP address of the bot. In addition, this host name will resolve to the IP address used. In order to validate if a google bot is "real", the lookup against .googlebot.com is required. An attacker could fake the reverse lookup if the attacker can provide reverse DNS for the IP address used by the attacker.

Personally, I use  a little shell script to extract "fake google" spiders from my logs:

 

#!/bin/sh
 
# you may need to adjut the "cut" parameter and file name to match your own log format.
for b in `grep 'Googlebot' /var/log/httpd/*access_log | cut -f 2 -d' ' | sort -u`; do
  h=`host $b`
  if echo $h | grep -e ' crawl-.*\.googlebot\.com\.$'; then
    h=`echo $h | cut -f5 -d' '`
    n=`host $h | cut -f4 -d' '`
    if [ "$n" = "$b" ] ; then
      echo ok $n $h $b
    else
      echo fake $b;
    fi
  else
    echo fake $b;
  fi
done

 

 

------

Johannes B. Ullrich, Ph.D.
SANS Technology Institute
Twitter

Keywords: google webapp
1 comment(s)
ISC StormCast for Monday, June 10th 2013 http://isc.sans.edu/podcastdetail.html?id=3356

Comments

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Dec 3rd 2022
9 months ago

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Dec 3rd 2022
9 months ago

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9 months ago

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Dec 26th 2022
9 months ago

Enter comment here... a fake TeamViewer page, and that page led to a different type of malware. This week's infection involved a downloaded JavaScript (.js) file that led to Microsoft Installer packages (.msi files) containing other script that used free or open source programs.
distribute malware. Even if the URL listed on the ad shows a legitimate website, subsequent ad traffic can easily lead to a fake page. Different types of malware are distributed in this manner. I've seen IcedID (Bokbot), Gozi/ISFB, and various information stealers distributed through fake software websites that were provided through Google ad traffic. I submitted malicious files from this example to VirusTotal and found a low rate of detection, with some files not showing as malware at all. Additionally, domains associated with this infection frequently change. That might make it hard to detect.
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