Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Vulnerabilities / Threats

3/27/2012
08:13 PM
50%
50%

Malware To Increasingly Abuse DNS?

Many companies do not scrutinize their domain-name service traffic, leaving an opening for malware to communicate using the protocol

Security researchers have looked at ways to abuse the domain-name service (DNS) for years. From denial-of-service attacks aimed at domain-name servers to various forms of domain hijacking, the DNS system is a perennial target of researchers and attackers alike.

Now some researchers are warning that the protocol may increasingly be used to help criminals communicate with compromised systems. At last month's RSA Conference, Ed Skoudis, a senior security consultant with InGuardians, predicted that more malware would hide its commands and exfiltrated data in DNS packets. The advantage for malware writers is that even if a company bars a potentially infected computer from contacting the Internet, malware could send DNS requests to a local server, which would then act as a proxy, bypassing defenses.


"With DNS as a command-and-control channel, as long as the internal machine can resolve names on the Internet, then there is command and control," Skoudis told attendees. "A machine could be blocked by sending outbound connections, so, instead, the machine sends a request to its internal DNS server, and that DNS server forwards onto the Internet, ultimately getting to the bad guy's server."

To date, the tactic has been relatively rare: Perhaps a dozen malware variants have used the domain-name system to send commands and updates to botnets. Skoudis cited two malware attacks that used a DNS channel as part of major breaches. Two relatively minor attacks -- PowPow and Wibimo -- have used the technique as well, according to Dell SecureWorks.

In all, around 5 percent of attacks contain some sort of DNS signaling, according to researchers at Internet Identity, a firm that specializes in securing Internet infrastructure and information. "It's the kind of communication that is not detected because most people are not watching DNS," says Lars Harvey, the firm's CEO.

The covert or malicious use of DNS for communications typically falls into two categories, says Gunter Ollmann, vice president of research at threat-protection firm Damballa. Tunneling uses the DNS port 53 to bypass firewalls that typically leave the port open so as not to interfere with domain lookups. The second technique hides data in DNS packets and uses the domain-name system infrastructure to transport the information to the destination chosen by the attacker.

It's the latter method that will be used more often, Ollmann says. Today, most command-and-control traffic is carried over the Hypertext Transfer Protocol (HTTP), but as defenders find ways of blocking the traffic, attackers will look for other possibilities.

"The bad guys are becoming more aware of how DNS is a weak spot in our defenses," he says. "And as other defensive technologies have improved inside enterprise networks, that particular door -- port 53 -- looks more attractive."

Detecting DNS is not that difficult, however. Sending communications over the domain-name system typically results in anomalous volumes of information, which is fairly easy to detect if a company is watching DNS. Ironically, the domain-name service security extensions, or DNSSEC, could make shipping data over DNS easier to hide. Normal DNS traffic has a limit of 512 bytes, while DNSSEC packets have no limit, so the protocol could be used to exfiltrate data from an unwary company's servers.

"If the volume of traffic is anomalous, any system that detects anomalies will detect it," Ollmann says. "If you do have deep-packet inspection capability, then you will detect the low and slow, once-a-week transmission of data."

At least one researcher argues that the difficulty in hiding covert DNS communications makes it unlikely that the use of the protocol will take off in the criminal underground. Communications are hard to hide inside DNS packets if a company is looking out for odd traffic patterns, says Joe Stewart, director of malware research at Dell SecureWorks.

"There is nothing incredible stealthy about it," he says. "It is hard to blend in with DNS traffic and pass a reasonable amount of data inside the packets."

Companies need to be watching their DNS traffic to make sure online thieves are not communicating with compromised systems or stealing data from the corporate network, researchers say. While logging all traffic is too onerous, companies should watch out for DNS traffic issued to parts of the world where they do no business and use traffic monitoring to look for anomalies.

Have a comment on this story? Please click "Add Your Comment" below. If you'd like to contact Dark Reading's editors directly, send us a message.

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
News
Inside the Ransomware Campaigns Targeting Exchange Servers
Kelly Sheridan, Staff Editor, Dark Reading,  4/2/2021
Commentary
Beyond MITRE ATT&CK: The Case for a New Cyber Kill Chain
Rik Turner, Principal Analyst, Infrastructure Solutions, Omdia,  3/30/2021
Register for Dark Reading Newsletters
White Papers
Video
Cartoon
Current Issue
2021 Top Enterprise IT Trends
We've identified the key trends that are poised to impact the IT landscape in 2021. Find out why they're important and how they will affect you today!
Flash Poll
How Enterprises are Developing Secure Applications
How Enterprises are Developing Secure Applications
Recent breaches of third-party apps are driving many organizations to think harder about the security of their off-the-shelf software as they continue to move left in secure software development practices.
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2015-20001
PUBLISHED: 2021-04-11
In the standard library in Rust before 1.2.0, BinaryHeap is not panic-safe. The binary heap is left in an inconsistent state when the comparison of generic elements inside sift_up or sift_down_range panics. This bug leads to a drop of zeroed memory as an arbitrary type, which can result in a memory ...
CVE-2020-36317
PUBLISHED: 2021-04-11
In the standard library in Rust before 1.49.0, String::retain() function has a panic safety problem. It allows creation of a non-UTF-8 Rust string when the provided closure panics. This bug could result in a memory safety violation when other string APIs assume that UTF-8 encoding is used on the sam...
CVE-2020-36318
PUBLISHED: 2021-04-11
In the standard library in Rust before 1.49.0, VecDeque::make_contiguous has a bug that pops the same element more than once under certain condition. This bug could result in a use-after-free or double free.
CVE-2021-28875
PUBLISHED: 2021-04-11
In the standard library in Rust before 1.50.0, read_to_end() does not validate the return value from Read in an unsafe context. This bug could lead to a buffer overflow.
CVE-2021-28876
PUBLISHED: 2021-04-11
In the standard library in Rust before 1.52.0, the Zip implementation has a panic safety issue. It calls __iterator_get_unchecked() more than once for the same index when the underlying iterator panics (in certain conditions). This bug could lead to a memory safety violation due to an unmet safety r...