Threat Level: green Handler on Duty: Jim Clausing

SANS ISC: Scanning for Single Critical Vulnerabilities - SANS Internet Storm Center SANS ISC InfoSec Forums


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Scanning for Single Critical Vulnerabilities

Where I work, we have a decent sized IP space and scanning can be problematic.  Within our IP space, we can have ~20 Million IP’s available.  Traditional scanning using NMAP, while effective, can take a long time even with aggressive scan setting.  By leveraging new scanning technologies like Masscan (hxxps://github.com/robertdavidgraham/masscan), this scanning can be done in minutes.  With moderate settings, I don’t want to crash firewalls, it takes about 15 min per port.

While this example is specific to Heartbleed, I use this technique for any of the exploit-of-the-day.  By using a fast port scanner to reduce the number of hosts to only the systems running the service in question, you can dramatically speed up your scan time. Additionally, within the first couple of days of an exploit,  you may be using a custom script to scan rather than a plugin from an enterprise solution.

Another use case is a vulnerability found during incident response.  If I determine a specific vulnerability was used to compromise a server, I then use this technique to determine other possible compromised systems. If they were not compromised, then we have them patch.

Masscan

Installing  the utility is easy

>git clone https://github.com/robertdavidgraham/masscan

>cd masscan/

>make; make install

Masscan uses a similar command line to nmap.

            >masscan -p 443,448,456,563,614,636,989,990,992,993,994,995,8080,10000

              10.0.0.0/8 -oG 10-scan-ssl - -max-rate 10000

 

-oG Grepable output

-p port to scan

10.0.0.0/8 network to scan

-oG Output in grepable format

10-scan-443 is filename created by scan

--make-rate sets the speed of the scan

Once Masscan has quickly identified targets for deeper inspection, you can use your more specific tool to determine if the system is vulnerable.  In this example, its an nmap plugin.

 

NMAP

cd /tmp

>svn co https://svn.nmap.org/nmap

>cd nmap

>./configure;make;make install


To get the input file in the correct format, use the following command to get just a file with a single IP per line.

            >grep -v '#' 10-scan-443 |awk '{print $2}' >/tmp/nmap

 

To run nmap, make sure you have the right ports specified, the specific script you need and specify the correct input file.

>nmap -p 443,448,456,563,614,636,989,990,992,993,994,995,8080,10000 --script=ssl-heartbleed.nse -iL /tmp/nmap -oA /tmp/ssl-vul-test


I've had mixed results with other scanners (scanrand ect..).  Any other large scale scanners with which you have had  good success?

--

Tom Webb

Tom

55 Posts
ISC Handler

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