DHS Issues Emergency Directive on DNS Security

All government domain owners are instructed to take immediate steps to strengthen the security of their DNS servers following a successful hacking campaign.

On Jan. 22, US-CERT issued notice of a CISA emergency directive on DNS infrastructure tampering. The notice was the typically brief CERT notice, but it linked to an emergency directive at that called on anyone managing .gov or other agency-managed domains to take a series of steps aimed at remedial efforts — and to take those steps very quickly.

"The fact that they put out the warning means that there's been some sort of successful breach against a government site that they're recovering from," says John Todd, executive director at Quad9. "This type of warning means that there's been some damage."

Marc Rogers, executive director of cybersecurity at Okta, agrees. "CERT puts out notifications on a regular basis, but I haven't seen one with such a strong sense of urgency before, which tells me that DHS is acting on actual knowledge of an ongoing attack," he says.

In the emergency directive, DHS said "attackers have redirected and intercepted web and mail traffic, and could do so for other networked services." The attacks began when someone stole, obtained, or compromised user credentials for an account able to make changes to the DNS records, the directive points out.

Most experts think the events alluded to in the emergency directive are related to a campaign of DNS attacks described by FireEye in a blog post dated Jan. 9. In that post, researchers said that attackers, most likely employed or sponsored by agencies in Iran, use a variety of techniques to gain access to and control over DNS servers. Once done, the result is activity that can compromise a variety of data and information types.

FireEye wrote that the attacks appeared to have begun as long ago as 2017, and prominently feature a technique first described by researchers at Cisco Talos in which the DNS "A" records are modified. This technique results in the attacker gaining a user's username, password, and domain credential, without producing any activity that would alert the user to a problem.

One of the ways in which attackers hide their activity is through the use of a counterfeit encryption certificate. "The attack described is heavily using 'Let's Encrypt,' which allows someone to easily get a certificate for a domain they control. The attackers went in, modified the records, then immediately got a certificate from Let's Encrypt, so people coming in from other domains won't get an error message," says Adnan Baykal, global technical adviser at the Global Cyber Alliance.

While the duration of the overall attack makes it highly unlikely that it was timed to take advantage of the current partial government shutdown, aspects of the shutdown have made it easier for the attack to succeed. "When you see that there are close to 100 certificates in federal domains that have expired during the shutdown, each one represents a serious risk for users who go to the site. This pushes up the risk of DNS hijacking," Rogers says.

Baykal agrees. "Visitors are getting browser errors, and people have no good way to tell whether the error is from an expired certificate or a spoofed certificate," he says.

These statements amplify the point that there's little for a site's visitors to do regarding possible DNS hijacking. "You need to use or have access to a validating recursive DNSsec resolver," Todd says. "You can use a service that tries to give me an accurate answer, and if it's not accurate, it fails the request." He notes, though, that most users rely on their ISPs' DNS servers, few of which use DNSsec validation.

As for the emergency directive's mandates, they include auditing DNS records, changing passwords for accounts that have DNS administration privileges, and putting two-factor authentication into service — and doing it all within 10 days. "All of the remediation makes perfect sense based on the FireEye report. You’d hope that they would have done so earlier, but that horse has left the barn," says Cricket Liu, executive vice president of engineering and chief DNS architect at InfoBlox.

And the mandates shouldn't be ignored by those who aren't bound by the government directives. "This is a wakeup call for anyone who owns a domain. Although the US government is issuing the order, anyone anywhere in the world should be paying a lot of attention," Todd says.

Liu agrees. "The things they're recommended are a good idea for anyone, whether you're part of the federal government or not," he says. "All of these are a good idea, regardless."

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