In its 2019 Sea Turtle investigation, Cisco Talos described attackers changing DNS records so legitimate domain names sent users to attacker-controlled infrastructure. That infrastructure could intercept credentials and traffic, then pass users on to the real service. The campaign used compromised DNS-related accounts and intermediary providers to reach high-value organizations. The reporting documents activity through the first quarter of 2019; it does not establish that the campaign is ongoing today.
How DNS hijacking redirects a legitimate domain
Domain Name System (DNS) translates a name such as an organization’s website into the network address a device should contact. In DNS hijacking, an attacker illicitly changes records so a legitimate name resolves to infrastructure the attacker controls. Cisco Talos described that mechanism in its April 17, 2019 Sea Turtle report.
The change can be made through an account or system authorized to manage DNS; it does not require malware on every visitor’s device. Talos reported spear-phishing and exploitation of known vulnerabilities as ways to gain an initial foothold. The attackers then altered name-server or address records. CISA’s Emergency Directive 19-01 described a related chain involving compromised credentials for an account able to change DNS, altered A, MX, or NS records, and redirection to attacker-controlled infrastructure.
- An attacker gains access to an account or system that can change DNS, potentially through phishing or exploitation.
- The attacker alters records or name-server settings so a target domain resolves to infrastructure under the attacker’s control.
- Users attempting to reach the legitimate service are redirected. The attacker can intercept credentials or traffic and may relay users to the real service afterward.
Because DNS changes can affect an organization’s services and their users at the naming layer, a user may not see an obvious sign that the destination has changed.
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Why HTTPS does not necessarily reveal the redirection
A browser’s HTTPS connection protects traffic to the server presenting a certificate trusted for the domain, but it does not by itself prove that DNS sent the browser to the intended server. CISA warned that control over DNS records could let an attacker obtain valid encryption certificates for an organization’s domain names. As the directive put it, “Because the attacker can set DNS record values they can also obtain valid encryption certificates for an organization’s domain names.”
That means HTTPS alone is not a reliable way to detect this kind of infrastructure compromise: a valid certificate or padlock may appear even when DNS has been manipulated. Detection requires attention to the systems that control domain records and to unexpected certificate issuance.
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What Talos reported about Sea Turtle
In its initial disclosure, Talos estimated that Sea Turtle likely began as early as January 2017 and continued through the first quarter of 2019. The investigation found at least 40 organizations in 13 countries compromised. Those are Talos’s 2019 findings, not a current tally.
The campaign targeted national-security organizations, ministries of foreign affairs, and prominent energy organizations. Talos also identified DNS registrars, telecommunications companies, and internet service providers among the secondary victims. Compromising those intermediaries gave attackers a route to reach higher-value primary targets.
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Talos assessed with high confidence that the activity was conducted by an advanced state-sponsored actor seeking persistent access to sensitive networks and systems. Its initial report did not publicly identify a particular government. A separate DNS-hijacking wave discussed in contemporaneous SecurityWeek coverage was attributed to Iran by FireEye; that separate reporting should not be treated as attribution of Sea Turtle.
What later reporting does—and does not—establish
On July 9, 2019, Talos reported that Sea Turtle activity had continued after the public disclosure, described additional victims including a country-code top-level-domain registry, and discussed another DNS-hijacking technique. Talos assigned only moderate confidence to the connection between that technique and Sea Turtle. This follow-up documents activity in 2019; it does not establish that the campaign remains active in 2026.
How organizations can protect DNS control
CISA issued Emergency Directive 19-01 on January 22, 2019 for covered U.S. federal agencies. It required four actions within 10 business days: audit public DNS records, change passwords for accounts that could alter agency DNS, implement MFA on those accounts, and monitor Certificate Transparency logs for certificates the agency had not requested. These were requirements for agencies covered by the directive, not universal legal obligations. CISA recommended phishing-resistant authentication factors and said SMS-based MFA was not recommended.
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Other organizations can adapt the underlying controls to their own domain-management arrangements:
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- Inventory every path to DNS changes. Include registrar, registry, authoritative DNS host, and identity accounts or support processes that can authorize a change.
- Verify expected records. Maintain an approved record set and check A, MX, and NS records for unauthorized changes.
- Harden accounts. Use strong, unique passwords and MFA, preferably a phishing-resistant method, on every account that can change DNS.
- Monitor changes and certificate issuance. Alert on DNS updates and review Certificate Transparency data for certificates for your domains that you did not request.
- Consider additional change controls. Registry locks and out-of-band confirmation can add friction against unauthorized changes, but their availability and implementation depend on the registrar or registry.
A FIDO2 security key is one possible form of phishing-resistant MFA for a DNS-management account when the account provider supports it. The control is the important point; CISA’s guidance does not endorse a particular product.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to investigate a suspected DNS change
For domain owners and administrators, compare live public DNS records with an approved baseline and check provider audit logs or account notifications for unexpected access and record changes. Review certificates issued for your domains through Certificate Transparency monitoring, and verify that any unfamiliar issuance was authorized. If a record or certificate change appears unauthorized, treat the DNS-management account and its provider access as potentially compromised: secure the accounts, contact the registrar or DNS provider through a known channel, and coordinate investigation and remediation with your security team.
Visitors generally cannot reliably determine from a browser alone whether an organization’s DNS infrastructure has been compromised. A valid HTTPS connection is not conclusive evidence that DNS resolution was legitimate. Report suspicious behavior to the organization through a separately verified contact route rather than entering credentials on a page whose destination is in doubt.
Quick Recap
Sources
- Cisco Talos, “DNS Hijacking Abuses Trust In Core Internet Service,” April 17, 2019.
- CISA, “Emergency Directive 19-01: Mitigate DNS Infrastructure Tampering,” January 22, 2019.
- Cisco Talos, Sea Turtle follow-up, July 9, 2019.
- SecurityWeek, contemporaneous coverage, April 18, 2019.
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