Vulnerabilities in Popular DNS Software Allow Poisoning

Seven flaws in DNSMasq have limited impact, but in combination they could be chained to create a multistaged attack.

4 Min Read

A group of vulnerabilities in the popular DNSMasq software used for domain name system (DNS) caching and IP address assignment could allow an attacker to reroute network traffic or use nearly 1 million open forwarders on the Internet for denial-of-service (DoS) attacks.

The vulnerabilities — found by Israeli security services firm JSOF and confirmed by large technology firms including Google and Red Hat — include three vulnerabilities that allow DNS cache poisoning and four buffer-overflow vulnerabilities. Dubbed DNSpooq, the vulnerabilities could redirect people using the vulnerable DNS forwarding service, referred to as DNS cache poisoning, or be used to take over the device, JSOF stated in an advisory.

While a DoS attack or device takeover could happen, DNS cache poisoning could also be used for fraud, says Shlomi Oberman, CEO at JSOF.

"If you browse to one website, but you are actually directed to another website — there could be all kinds of fraud," he says. "The worse-case scenario is cache poisoning and a remote execution attack."

A collection of software and device makers have tackled the issues in a working group for months. The vulnerabilities affect software and network appliances from at least 16 vendors, including Cisco, Digi International, Netgear, Red Hat, and Siemens. DNSMasq, which was authored by network expert Simon Kelley, patched the issues about four weeks ago but released the update — version 2.83 — on Sunday, according to the project's log files

The cache poisoning flaws make a redirection attack more probable but not certain, according to statements by Red Hat in its advisory.

"These flaws substantially reduce the number of attempts an attacker has to make to guess the 16-bit identifier and the specific UDP port used for a particular DNS query," the company states. "Considering the attack is not deterministic and requires some time to guess the right combination of values, an attacker needs a dnsmasq client to start performing many DNS queries to an attacker-chosen domain."

The attack has some relation to widespread vulnerabilities found in DNS software more than 13 years ago. Unlike the more recent issues, those vulnerabilities — found by security research Dan Kaminsky — were caused by design issues that could be exploited in concert. While there have not been attacks in the wild using the latest set of vulnerabilities, attackers started using the Kaminsky vulnerabilities in attacks within the month, suggesting the utility of cache poisoning flaws may make them a high-priority issue.

The threat posed by the vulnerabilities is uncertain. In the past, home users rarely, if ever, patched their routers. Some Internet service providers and device vendors have improved their patching process, but patching is still very spotty, Shlomi says. 

"This is relatively easy to pull off, and home routers are not updated that frequently," he says. "So home networks will likely be attacked."

Android devices also use DNSMasq for routing network traffic when in hotspot mode, Shlomi says. Attacking those devices would require proximity, limiting the impact of the vulnerabilities.

Companies, however, have to worry about workers connecting from home to the business network and cloud services but who may have a vulnerable home router. The lack of visibility most companies have into the current distributed workforce's security posture will likely make the vulnerabilities harder to eradicate. And workers who connect to the corporate network through a virtual private network could give an attacker a bridge into the network, Shlomi says. 

"Remote work makes it a lot more difficult," he says. "Oftentimes, browsing to just your corporate website may not be as secure as browsing to sites on the Internet because their certificate might be self-signed or not valid."

Companies also have to worry about attackers gaining the ability to use the Internet's open DNS forwarding servers to route traffic into a distributed denial-of-service (DDoS) attack against a specific target. 

"Calculations show that the size of the attack could be on the same order of magnitude as the biggest DDoS attacks performed to date," JSOF stated in its analysis.

About the Author(s)

Robert Lemos, Contributing Writer

Veteran technology journalist of more than 20 years. Former research engineer. Written for more than two dozen publications, including CNET, Dark Reading, MIT's Technology Review, Popular Science, and Wired News. Five awards for journalism, including Best Deadline Journalism (Online) in 2003 for coverage of the Blaster worm. Crunches numbers on various trends using Python and R. Recent reports include analyses of the shortage in cybersecurity workers and annual vulnerability trends.

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