The Department of Homeland Security has issued an emergency directive ordering administrators of most federal agencies to protect their Internet domains against a rash of attacks that have hit executive branch websites and email servers in recent weeks.
The DHS’ Cybersecurity and Infrastructure Security Agency (CISA) issued the directive on Tuesday, 12 days after security firm FireEye warned of an unprecedented wave of ongoing attacks that altered the domain name system records belonging to telecoms, ISPs, and government agencies. DNS servers act as directories that allow one computer to find other computers on the Internet. By tampering with these records, attackers can potentially intercept passwords, emails, and other sensitive communications.
“CISA is aware of multiple executive branch agency domains that were impacted by the tampering campaign and has notified the agencies that maintain them,” CISA Director Christopher C. Krebs wrote in Wednesday’s emergency directive. He continued:
Using the following techniques, attackers have redirected and intercepted web and mail traffic, and could do so for other networked services:
1. The attacker begins by compromising user credentials, or obtaining them through alternate means, of an account that can make changes to DNS records.
2. Next, the attacker alters DNS records, like Address (A), Mail Exchanger (MX), or Name Server (NS) records, replacing the legitimate address of a service with an address the attacker controls. This enables them to direct user traffic to their own infrastructure for manipulation or inspection before passing it on to the legitimate service, should they choose. This creates a risk that persists beyond the period of traffic redirection.
3. Because the attacker can set DNS record values, they can also obtain valid encryption certificates for an organization’s domain names. This allows the redirected traffic to be decrypted, exposing any user-submitted data. Since the certificate is valid for the domain, end users receive no error warnings.
To address the significant and imminent risks to agency information and information systems presented by this activity, this emergency directive requires the following near-term actions to mitigate risks from undiscovered tampering, enable agencies to prevent illegitimate DNS activity for their domains, and detect unauthorized certificates.
Krebs went on to direct administrators to take the following steps in the next 10 business days: