glenscott.net

Here are a couple of tools I wrote in python to parse and merge/ join Nmap .xml report files.

TL;DR:

• gnxparse.py outputs discovered host, port info from nmap .xml, optionally in the form of nmap command(s) to re-scan hosts.
• gnxmerge.py glues multiple (<host> sections from) nmap XML reports together.
• You can download them from the git repo here.

Problem:

Nmap is great for network auditing. Scanning from an internal, privileged, and/or fast network location (eg inside your firewall) is straightforward and fast, but doesn’t give you the whole picture – which discovered hosts and services are exposed from a different – eg external/public network.

To get this info, you could do a firewall config audit, but if you don’t have this access or just want to do a functional test of the firewall, you need to run another scan. For the same accuracy, you’ll want the full range (1-65535) portscan, and this takes time. Also, this kind of scan is noisy and may generate a lot of firewall/ips logs. Lastly, if you traverse an IPS/IDS with such a noisy scan, it may drop you as malicious, and the rest of the results are lost.

Solution:

An alternative approach is to do a full scan internally, and use the results to make a much quieter external scan targeting only known live hosts and services. gnxparse.py can generate nmap ‘rescan’ commands to run from outside the firewall, and gnxmerge.py helps tidy up the results by merging the multiple output files back into a single report.

The workflow goes something like this:

1. Perform a thorough scan of your publically routable subnets from a location inside the firewall. (Using some fairly well tuned host discovery options in nmap, it takes me about 3 hours to scan the full port range on ~1000 hosts on a fast internal network.)
2. Run gnxparse.py with the ‘rescan’ option on the .xml file generated from the internal nmap scan. This will output a bash script with individual nmap commands to probe only those hosts and services found to be up.
3. Copy the script to an external host with nmap and run it. (For all discovered services on the ~1000 hosts scaned earlier, it takes me only about five minutes to do a re-scan).
4. Run gnxmerge.py on the folder of individual .xml reports generated (one per host) if you need to produce a single Nmap XML report file for any reason, for example to load up in Zenmap[1] and review which of your services are exposed externally.

Hopefully someone else finds these tools useful. You can download  gnxparse.py and gnxmerge.py from my GNXTools repo on bitbucket.

[1] I am aware Zenmap can also load multiple nmap report files for viewing; though it does not merge/save.