An Essential Sys Admin and Security Tool

Wireshark as a Sys Admin Tool

It’s true that Wireshark is a security tool, but you can also use it as a pure system administration tool as well. It’s also true that many system administrators lead a double life as security administrators on smaller networks and in certain specialized workgroups on larger ones. In either case, here are a few ways that system administrators use Wireshark.

You want to find users who use non-approved cloud applications like Dropbox, because they can be used for exfiltrating data from the network. Open Wireshark and start a capture. Look for an entry in Figure 7 that displays the following line

Dropbox LAN sync Discovery Protocol

and check the associated IP address. In this case, 192.168.1.76 is the culprit. On this small network, I know that my wife’s computer has Dropbox installed and that LAN sync is activated. Most Dropbox users don’t realize that this service gives them away on a network, because the LAN sync Discovery Protocol looks for other systems to sync with on the local network.

Figure 7: A Wireshark scan showing Dropbox LAN sync Discovery Protocol entries.

System administrators can also detect illegal peer-to-peer network traffic, malicious exfiltration, and clear text communications using Wireshark. Having Wireshark as a tool can help you to know which malicious or undesirable protocols to block on network-managed host firewalls. Remember to establish a clear separation of duties and boundaries with your security department personnel. It’s troublesome to have too many port scanners and sniffers going at the same time, because such traffic can look like attacks from within the network. Cooperation is key to a safe, secure network and to stability for your users.

Wireshark as a Security Tool

A good example of using Wireshark as a security tool is to find out if there’s anyone on your network running a port scanner. It’s easy to find someone probing you when you have Wireshark open. See if you can find the scans and the originating computer in Figure 8.

Figure 8: Wireshark screenshot of a remote system port scan.

The SYN packets you see are NMAP probes. NMAP sends these packets to find out which ports on a remote system are open. In Wireshark, these types of scans are obvious. The originating IP address, 192.168.1.81 in this case, is the probing system. Depending on who owns the system with the .81 address will determine whether this is a friendly sweep or a malicious reconnaissance probe. Chances are good that the source address is spoofed if it’s a real attacker.

Conversely, how would you like to see who on your network might be using Wireshark or a similar tool to sniff network traffic? Well, you can do that with NMAP. In the example below, the target system is 192.168.1.68, but you can just as easily use a generic 192.168.1.0/24 to scan the entire range of a subnet.

nmap -sV --script=sniffer-detect 192.168.1.68
Starting Nmap 7.70 ( https://nmap.org ) at 2019-02-13 19:56 CST
Nmap scan report for 192.168.1.68
Host is up (0.00073s latency).
Not shown: 999 filtered ports
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 7.4 (protocol 2.0)
MAC Address: F8:CA:B8:2D:E1:18 (Dell)

Host script results:
|_sniffer-detect: Likely in promiscuous mode (tests: "11111111")

Service detection performed. Please report any incorrect results at 
  https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 7.94 seconds

Look back at the ping flood example in Figure 6. A ping flood is an attempt at a denial of service attack, because it floods both incoming and outgoing traffic -- incoming pings and outgoing replies. Properly configured routers and switches can prevent ping floods, but some internal network floods can still be effective for short periods of time. These attacks are generally short in duration, because they’re generally detected by network monitoring or security sweeps.

Conclusion

To use Wireshark and its many powerful capabilities, you need to practice with it on a live network. I suggest using a VLAN isolated test network to test ping floods, NMAP scans, brute force attacks, and other malicious traffic examples so that you become familiar with them. Typically, Wireshark scans are used for snapshotting network traffic either during times of alleged attacks, to check suspicious traffic, or to establish network traffic baselines.

Wireshark is neither a SIEM nor is it a network security panacea. It is powerful and can do many things, but it cannot be everything. It is primarily a network protocol analyzer and should be used as such and in concert with other security and system administration tools. As with any set of tools in a toolbox, it is only one of many, and none is more useful or better than any other.

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