Dutch ISP Ziggo demonstrates how not to inform your customers about a security flaw

Dutch ISP Ziggo demonstrates how not to inform your customers about a security flaw

“Can you have a look at this email I got, please?” my brother asked. “It looks convincing enough, but I don’t trust it,” he added and forwarded me the email he received from Ziggo, his Internet Service Provider (ISP). Shortly after, he informed me that despite its suspicious aura, he found confirmation that the email was, in fact, legitimate.

In the suspect email, the Dutch ISP informed customers that an expert had found a weakness in the “Wifibooster Ziggo C7,” a device they sell to strengthen WiFi signals. Ziggo told users how to recognize this equipment, and urged them to change the default password and settings.

So what’s the problem? Alerting customers about a security flaw is best practice, is it not? Absolutely. But when your email alert about a security vulnerability looks like a phish itself, it’s time to reevaluate your email marketing strategy.

In this blog, I’ll break down what exactly happened with Ziggo, the flaws in their email communication, and how organizations should approach informing their employees and customers about potential security issues—without looking like a phishing scam.

What exactly happened?

Dutch ISP Ziggo sent out an email to their customers warning about a security weakness in a specific device that they sell to their customers. I translated the relevant parts of the mail from Dutch below:

“Dear Mister Arntz,

To keep our network safe, experts are looking for weak spots. Unfortunately, such a weakness was found in the Wifibooster Ziggo C7. You can recognize the device by the ‘C7’ mark at the bottom. This email is about this device and this type only.

Do you indeed use the Wifibooster Ziggo C7? In that case change the default settings in your personal settings to keep your device safe. Below we will explain how.

How to change your password

To make the chance of abuse as small as possible, it’s necessary to change your password. Go to link to Ziggo site, follow the instructions there and use a strong password.

Want to know more or need help?

Follow the link to the Ziggo forum where you can find more information about this subject and ask for help from the community members.”

This vague, unhelpful, and frankly dangerous advice was followed by a footer that contained nine more links, including (ironically enough) an anti-phishing warning.

What made the email look spammy?

We have spent years training people to recognize spam emails, and it is gratifying when our efforts pay off on occasion. The things my brother mentioned he found to be spammy were all the weird looking links in the email and the fact that he did not own the device that was the subject of the email.

I would like to add that the email mentioned a security weakness but did not specify which one. Also, the urge to change your password to avoid danger would be a dead give-away in a phishing mail.

So, we’ve got:

  • Subject does not apply directly to all receivers. Not every addressee had said device. When asked Ziggo stated they wanted to make sure that users that bought the device second-hand would be aware of the issue too.
  • A multitude of links that looked phishy probably because they were personalized.
phishy looking link
  • Urging receivers to go to a site and take precautions against an unclear threat.

The device

The Wifibooster Ziggo C7 is in fact a TP-Link Archer C7 that Ziggo sells to their customers with their own firmware installed. Therefore, it is hard to find any information about what the vulnerability might be. The Archer C7 is listed as affected by the WPA2 Security (KRACKs) vulnerability for certain firmware versions. But given the Ziggo device comes with custom firmware, it is hard to determine whether the Wifibooster Ziggo C7 is vulnerable as well.

Based on the fact that users are urged to change their wifi-passwords and the name of the network (SSID) and looking at the instructions we found on the site we are inclined to conclude that the device was shipped with default credentials, which might help attackers to exploit a remote acces vulnerability.

The possible danger

Ziggo warned the users that not following their instructions could lead to unauthorized access to their network.

We asked our resident hardware guru JP Taggart about this scenario and he was very weary about ISPs that put more than some branding deviations of the manufacturer’s firmware on the device. Once you start to drift away from the standard firmware you are responsible for maintaining and patching that firmware, because the manufacturer will no longer be able to or even want to. We have looked at some existing vulnerabilities for the Archer C7 but they are old and if they would apply it couldn’t be cured by changing the password and SSID.

ISPs make a habit of branding the firmware for the equipment they sell to their customers. Logic dictates that the security flaw must have been in this branded firmware, since we could not find any other recent warning about this particular type of device. Which would demonstrate JP Taggarts’ comment about the dangers of branded firmware.

What Ziggo could have done better

The most objectional part of the method Ziggo chose to inform is the phishy looking format they constructed their email in. The more companies do this, the harder it is for us to tell the real phishes apart from the legitimate emails. To be honest, some of the more sophisticated phishers have produced emails that looked less phishy than this one.

They also could have been a lot more open about the security flaw that was found. Of course we don’t expect them to post a full hackers guide on how to use an exploit and spy on your neighbor, but a little bit of concrete information on what was found and how that could be exploited would have made sense.

For the instructions of how to change the settings I would have found it preferable to list the basic steps in the email and include a link for those that need further or more detailed instructions. All the relevant and necessary information should have been in the mail and not been linked to. Links are fine, but not for crucial information.

During the installation of such a device the ISP should force the user to change the default password at least, and probably advise them to change the SSID as well. A default SSID tells an aspiring hacker which ISP you are using and they can make some informed guesses at which equipment you are using etc.

The danger of sending out phishy emails

Invested parties may have deleted the mail at first sight and never changed their password, making them vulnerable to the ‘flaw”.

Or, as our own William Tsing wrote in an older post called When corporate communications look like a phish:

“Essentially, well-meaning communications with these design flaws train an overloaded employee to exhibit bad behaviors—despite anti-phishing training—and discourage seeking help.”

This is also true for the home user that may not receive as many emails at home as an office employee does (120), but the ones that do receive a lot of mail, have trained themselves to recognize the emails that are important and ignore the rest. Which would be a shame if the included information is as important as the ISP wants us to believe.

Stay safe, everyone!


Pieter Arntz

Malware Intelligence Researcher

Was a Microsoft MVP in consumer security for 12 years running. Can speak four languages. Smells of rich mahogany and leather-bound books.