Free, public Wi-Fi is now crucial in ensuring people stay connected where a secure network is absent or mobile data is unavailable. While the advantages of flexible internet access are obvious, the dangers are often less clear. By now, most of us are aware that these networks can pose a risk, but few can articulate exactly what these risks are and how we can protect ourselves. Follow the advice below to find out exactly what dangers lurk within.
The perils of public wi-fi
When you join a public hotspot without protection and begin to access the internet, the packets of data that go from your device to the router are public and open for anyone to intercept. While that sounds scary, technology like SSL/TLS has ensured the danger here isn’t as bad as it was a few years ago. That being said, all a cybercriminal needs to snoop on your connection is some relatively simple Linux software that’s accessible online.
This leaves you vulnerable to a variety of attacks. Let’s take a look at some of them now.
Typically, a wi-fi adapter will be set on “managed” mode. This means it acts as a standalone client connecting to a single router for access to the internet. The interface will ignore all data packets except those that are explicitly addressed to it. However, some adapters can be configured into other modes. In “monitor” mode, an adapter will capture all the wireless traffic in a certain channel, regardless of the source or intended recipient. In this mode, the adapter can even capture data packets without being connected to a router – meaning it can sniff and snoop on all the data it gets its hands on.
Not all commercial wi-fi adapters are capable of this, as it’s cheaper for manufacturers to make those that only handle “managed” mode. Still, if someone gets their hands on one and pairs it with some simple Linux software, they can see which URLs you are loading and all of the data you’re entering on any website not using HTTPS – including names, addresses, and financial accounts.
Catching unencrypted data packets out of the air isn’t the only risk of public wi-fi. When you connect to an unprotected router, you are implicitly trusting the supplier of that connection. Usually this trust is well-founded – it’s unlikely your local café is interested in your private data. However, the carelessness with which we now connect to public routers means that cybercriminals can easily set up a fake network to bait you in.
Once an illegitimate hotspot has been created, all of the data flowing through it can be captured, analysed, and manipulated. One of the most common forms of manipulation is simply redirecting your traffic to an imitation of a popular website. The sole purpose of this clone site will be to capture your personal information and card details – the same strategy used in phishing scams.
Unfortunately, cybercriminals don’t even need a fake hotspot to interfere with your traffic.
Every wi-fi and Ethernet network has a unique MAC address – an identifying code used to ensure data packets travel to the correct destination. The way that routers – and all other devices – discover this information is using ARP (Address Resolution Protocol).
For example, your smartphone might send out a request asking which device on the network is associated with a certain IP address. The requested device responds with its MAC address, ensuring the data packets are physically directed to the correct location.
The issue with ARP is that it can be faked. Your smartphone might send a request for the address of the public wi-fi router, and a different device will answer with a false address.
Providing the signal of the false device is stronger than the legitimate one, your smartphone will be fooled. Again, this can be done with simple Linux software.
Once the spoofing has taken place, all of your data will be sent to the false router, which can subsequently manipulate the traffic however it likes.
Man-in-the-Middle (MitM) attacks
A man-in-the-middle attack (MITM) refers to any malicious action in which the attacker secretly relays or alters the communication between two parties. On an unprotected connection, a cybercriminal can modify key parts of the network traffic, redirect this traffic elsewhere, or inject content into an existing packet.
This could mean displaying a fake login form or website, changing links, text, pictures, or more. This is relatively straightforward to execute; an attacker within reception range of an unencrypted wi-fi point could insert themselves easily.
How to secure your connection
The prevalence and simplicity of these attacks only serves to highlight the importance of basic cybersecurity best practices. Following these foundational rules of cybersecurity should serve to counteract the vast majority of public wi-fi threats.
An effective firewall will monitor and block any suspicious traffic flowing to and from your device. It’s a given that you should always have a firewall in place and your virus definitions updated to protect your device from upcoming threats.
Though properly configured firewalls can effectively block some attacks, they’re not infallible, and do not exempt you from danger. They primarily help protect against malicious traffic, not malicious programs, and may not protect you if you inadvertently run malware. Firewalls should always be used in conjunction with other protective measures such as antivirus software.
Not to be underestimated, software and system updates are imperative and should be installed as soon as they’re offered. Staying up to date with the latest security patches is the simplest step in protecting yourself against existing and easily-exploited system vulnerabilities.
Use a VPN
Whether you’re a regular user of public Wi-Fi or not, A VPN is an essential security tool worth having. This software works by generating an encrypted tunnel that all of your traffic travels through, ensuring your data is secure regardless of the safety of the network you’re on. This is paramount for anyone concerned about their security online, and is arguably the best safeguard against the risks of open networks.
That being said, there are dozens of available VPN services, many of which are unreliable or even dangerous. Free VPN providers have been known to monitor and sell users’ data to third parties. It’s important you choose a service provider with a strong reputation and a strict no-logging policy. It’s a crowded market, but most review websites recommend ExpressVPN and NordVPN as reliable options.
Use common sense
If you find yourself with no option but to use public Wi-Fi without a VPN, the majority of attacks can be avoided with old-school safe computing practices. Avoid making purchases or visiting sensitive websites like online banking. It’s best to stay away from any website that doesn’t use HTTPS. Luckily, popular browser extensions like HTTPS everywhere can help extend your reach.
The majority of modern browsers have in-built security features that can identify threats and notify you if they encounter a malicious website. While it’s sensible to heed these warnings, these browsers are not failsafe and are much less likely to spot local interference by an unknown third party.
Simple solutions are often the strongest in cybersecurity
With the rising use of HTTPS and TLS, it’s become much harder for data to be intercepted and exploited. That being said, with a laptop, free Linux software, and a cheap Wi-Fi adapter, you’d be surprised how much damage can be done.
Public Wi-Fi is now a staple of modern life. Despite its ubiquity, it’s still exploited with relative ease, and many are oblivious to exactly what these risks entail. Clearly cybersecurity still has a long way to go at the consumer level; for now, old lessons still ring true – the simplest solutions are often the strongest.
William Chalk is a writer and researcher at Top10VPN, a cybersecurity research group and the world’s largest VPN (Virtual Private Network) review site. As well as recommending the best VPN services, they publish independent research to help raise awareness of digital privacy and security risks.