Researchers at Infoblox and Eclypsium have discovered that a powerful attack vector in the domain name system (DNS) is being widely exploited across many DNS providers. The researchers found that over a dozen Russian-nexus cybercriminal actors are using this attack vector to hijack domain names without being noticed. We call this the Sitting Ducks attack.
There are over a million exploitable target domains on any given day, and the attack is easy to perform, almost totally unrecognised, difficult to detect, and entirely preventable.
In a Sitting Ducks attack, the actor hijacks a currently registered domain at an authoritative DNS service or web hosting provider without accessing the true owner’s account at either the DNS provider or registrar. Once the actor has control of the domain, they can conduct any form of malicious activity under the guise of the legitimate owner. This includes malware delivery, phishing campaigns, brand impersonation and data exfiltration. Exploitable domains are not rare. Infoblox estimates that over a million domains are exploitable on any given day, and we have identified multiple methods to identify vulnerable domains.
The researchers discovered Sitting Ducks while studying the infrastructure used for the so-called 404TDS, a Russian hosted traffic distribution system (TDS) first identified by Proofpoint. The domains used for this TDS were clearly hijacked, but the breadth of registrars and domain owners involved created a perplexing picture. That is, until Infoblox discovered the threat actor’s method. They initially thought the attack vector was unpublished. Recently the researchers learnt that Matt Bryant had previously described the attack vector in his blog, The Hacker Blog, both in August and December 2016. Two years after his initial advisory, Sitting Ducks was used to hijack thousands of domains for use in a series of global spam campaigns that included bomb threats and sextortion.
Eight years after it was first published, the attack vector is largely unknown and unresolved. Sitting Ducks is easier to perform, more likely to succeed, and harder to detect than other well-publicised domain hijacking attack vectors, such as dangling CNAMEs. At the same time, Sitting Ducks is being broadly used to exploit users around the globe. Infoblox’s analysis showed that the use of Sitting Ducks has grown unabated over several years and is unrecognised in the security industry.
At the heart of Sitting Ducks attacks are incorrect configurations at the domain registrar and the inadequate prevention at the DNS provider, both of which are solvable problems. There are several variants of the Sitting Ducks attack, none of which require the attacker to register a domain themselves, making it fundamentally different from commonly discussed DNS hijacking attacks.
Attackers can use the Sitting Ducks attack vector under the following conditions and in several variations:
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A registered domain or subdomain of a registered domain uses or delegates authoritative DNS services to a different provider than the domain registrar; this is called delegation.
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The delegation is lame, meaning that the authoritative name server(s) of the record does not have information about the domain and cannot, therefore, resolve queries
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The authoritative DNS provider is exploitable, meaning that the attacker can “claim” the domain at the provider and set up DNS records without access to the valid owner’s account at the domain registrar.
Variations within this attack include partially lame delegation and redelegation to another DNS provider. While these conditions may seem unusual, they are not. Multiple threat actors are actively exploiting this attack vector, and we expect the true exploitation to be larger than is currently known.
Although a Sitting Ducks attack is easy at many popular DNS and website hosting providers, some providers are not exploitable. Infoblox performed a large-scale analysis of domain delegations, evaluated about a dozen DNS providers and uncovered widespread use of the attack, most prominently by Russian cybercriminals. Hundreds of domains are hijacked every day, and Infoblox is tracking multiple actors who use this attack.
InfoBlox found hijacked and exploitable domains across hundreds of TLDs. Hijacked domains are often registered with brand protection registrars; in many cases, they are lookalike domains that were likely defensively registered by legitimate brands or organisations. Because these domains have such a highly regarded pedigree, malicious use of them is very hard to detect.
Unlike many other types of cybercrime, Sitting Ducks attacks are preventable. The attack is possible because of gaps in how domain names and DNS records are managed, maintained, and authorised. Prevention requires everyone to play a part: domain name holders, registrars, authoritative DNS providers, web hosting providers, standards bodies, government regulators, and the cybersecurity community.
Inflobox’s discovery of the Sitting Ducks attack leveraged reporting by Proofpoint, independent research by Randy McEoin, and contributions from David Safley. InfoBlox began ethical disclosure notification shortly after validating the attack vector.
Exploitation in the Wild
The researchers discovered over a dozen seemingly different threat actors conducting Sitting Ducks attacks on several exploitable authoritative DNS services. Each of these has some Russian nexus, and one might argue that certain DNS providers have become a veritable Russian cybercriminal playground that has been allowed to grow unchecked for years. Infoblox research revealed that the Sitting Ducks vector has been used to hijack over 35,000 domains since 2018, although the true number is likely much higher. The earliest known threat actor is Spammy Bear, who appears to have begun hijacking domains in late-2018 at GoDaddy. However, many more providers are exploitable, and we have confirmed hijacking on six DNS providers to date.
Often, a single domain was hijacked by different actors over time. Some exploitable DNS providers are being treated as a “domain lending library,” where threat actors use free accounts to “borrow” a domain for 30-60 days at a time. The rotational use by different actors creates additional obfuscation that makes Sitting Ducks hard to detect. In other cases, an actor has hijacked domains at DNS providers that do not offer free accounts. Similarly, while those with free accounts are typically hijacked for short periods of time, we Infoblox has seen threat actors hold a domain for over a year. Frequently, the hijackers host the stolen domains on notorious Russian providers such as Stark Industries and Evil Empire. Threat actors have obtained SSL certificates for the domains in many cases, both from free services like Let’s Encrypt and paid services like DigiCert.
There are two sets of victims in Sitting Ducks exploitation: the true domain name owners and the targets of malicious activity.
Both types of victims vary widely. While a large percentage of the hijacked domains are owned by large brands, many of them belong to small businesses and individuals. Some were registered by regional and local governments. In many cases, the domains seem to have been configured to auto-renew at the registrar, but the authoritative DNS or hosting services were not renewed. We have even seen actors use the Sitting Ducks vector to hijack domains from other threat actors.
Once the malicious actor has control of the domain at the name server, they can do whatever they like with it, and analysis of confirmed exploitation indicates that the hijackers have done all manner of bad things.
There are multiple traffic distribution systems (TDSs) operating on stolen domains using the Sitting Ducks attack. The operators of a TDS serve a criminal customer base, and the role of a TDS provider, like a traditional ad broker, is to connect potential victims to malware, phishing, or scams that suit their victim profile. In addition to the threat actor behind 404TDS, who we call Vacant Viper, the researchers have seen VexTrio Viper hijack domains at multiple DNS services. A special form of TDS, there are multiple malicious link shortening services built on hijacked domains.
Vacant Viper began using Sitting Ducks in December 2019, and has hijacked approximately 2500 domains each year. In addition to use in 404TDS, they use the stolen domains for spam operations and what appears likely to be command and control (C2) domains. VexTrio first hijacked a domain using Sitting Ducks in early 2020, and several of their affiliates also use the attack vector. TDSs are particularly dangerous as they facilitate cybercrime for hundreds of actors. Vacant Viper is known to affiliate with TA571, for which the 404TDS delivered IcedID and other malware. VexTrio Viper runs the largest and oldest known TDS with over 165 affiliates, including SocGholish and ClearFake. Infoblox has discovered multiple other as yet unnamed actors using Sitting Ducks to create a TDS.
Hijacked domains have also been used directly in phishing attacks and scams, as well as large spam systems. One threat actor appears to use the domains exclusively for shipping-related fraud. Multiple actors are using the domains to distribute porn or dating-related content. There is evidence that some domains were used for Cobalt Strike and other malware command and control. Other attacks have used hijacked domains in targeted phishing attacks by creating lookalike subdomains. A few actors have stockpiled hijacked domains for an unknown purpose.
One of the most active threat actors we have discovered hijacks domains from multiple DNS providers. They distribute investment scams through Facebook ads and possibly other mediums. These ads have targeted over thirty countries and often use lures of government infrastructure programs and investment summits. We intend to publish more about this actor and their history soon.
A Vulnerable Attack Surface
Sitting Ducks is a pernicious attack that is fundamentally different from other well-publicised techniques designed to take control of domains or subdomains. It requires no access to the registrar and is extremely hard to detect or distinguish from credential theft. Indeed, Infoblox assumed for several months that the hijacking conducted by an actor we were tracking was due to credential theft at the authoritative DNS provider.
The earliest known description of Sitting Ducks was in August 2016 by Matt Bryant. Infoblox also unearthed a handful of other reports that included special cases or variations of the attack vector.
Group-IB published a special case of Sitting Ducks via Russian media outlets in November 2020. The attack they describe involves a lapse in the web hosting provider service, whereas we have observed Sitting Ducks attacks that abuse vulnerable authoritative DNS providers in addition to web hosting providers. According to Group-IB’s blog, the attack vector was reported to Russian registrars and hosting providers, regional registrars, and unnamed international hosting providers. Unfortunately, like Bryant’s alerts in 2016, the attack was not picked up by mainstream media, or in the Russian case, widely reported to the international community.
Sitting Ducks is only the latest example of how attackers exploit misconfigurations in DNS. While DNS serves as the backbone for internet communication, it is often overlooked as a strategic attack surface. Published attack vectors against DNS may be dismissed as inevitable and not receive the same level of mitigation as a software bug, creating a perfect attack surface for malicious actors. Most recently, a default configuration by Squarespace left domain names acquired from Google vulnerable to hijacking.
In DNS, a lame delegation occurs when a name server is delegated, or assigned, to provide authoritative DNS records but does not have the information to do so. In certain cases, the registration for the delegated name server may have expired. A lame delegation attack occurs when the malicious actor registers the expired name server’s domain name. In this attack, the actor gains control of all domains that point to that name server. In addition to expired name server domains, this attack can leverage typos made by the domain owner when entering their name server information at the registrar. Researchers released an extensive study of the lame delegation attack surface in 2021.
During Infoblox’s research on Sitting Ducks exploitation, researchers identified multiple active attacks using typosquat name server domains. These attacks require the actor to register a domain but can be very effective, especially when the delegation is only partially lame, meaning that only some of the name servers are incorrectly configured.
While lame delegation attacks take advantage of faulty name server record assignments, these attacks can be generalised to other DNS record types. A dangling DNS record generally refers to a record containing invalid information, typically due to a forgotten configuration. For example, a dangling CNAME attack takes advantage of DNS CNAME records in which the DNS response “redirects” to a domain name whose registration has lapsed. In this attack scenario, the malicious actor registers the lapsed domain and gains pedigree through the forgotten record. Dangling CNAME attacks typically involve subdomains and are considered a type of subdomain hijacking attack. These attacks are actively used by actors and were the subject of recent reporting by Guardio Labs. Dangling CNAME attacks require the actor to register a domain.
Other types of dangling DNS records can be used to hijack domains. Where a subdomain points to a cloud resource that is no longer in use, an attacker may be able to gain access to this resource. Certitude Consulting detailed several examples of this attack in a recent report. During the research, Infoblox found several instances of dangling A records, some dating back more than five years. These attacks require the attacker to gain access to the hosting resource.
Chinese academic researchers have published multiple studies of dangling DNS records and outlined specific methods for identifying exploitable domains. Their papers include dangling CNAME attacks, attacks against cloud hosting providers and special cases of a Sitting Ducks attack. While these papers do not include active exploitation, they do outline the dangers of dangling DNS records and lame delegation.
Domain shadowing is another form of attack that might be confused with Sitting Ducks. This type of attack was highlighted by the US Cyber and Infrastructure Security Agency (CISA) in 2018. The attack allows the malicious actor to create new DNS records within the valid owner’s account. Domain shadowing attacks require the actor to access the existing account at the registrar or the DNS provider. Domain shadowing attacks rely on credential theft and is fundamentally different from DNS delegation or record attacks.
Finally, in 2021, researchers demonstrated that in certain cloud providers they could poison the DNS resolution path and gain access to sensitive internal DNS traffic. Their work focused specifically on Amazon Web Services (AWS). While the researchers did not find active exploitation of the weakness, it highlighted the complexities of delegated name server management for providers. AWS fixed this issue before publication, and it has not been reported as a vector for other providers.
