Internet Scan in 45 Minutes

Tuesday, August 20, 2013 @ 04:08 PM gHale


A new tool is capable of scanning the entire IPv4 address space in less than an hour.

There have been Internet-wide scans done by various organizations over the years, but most of them have not had a security motivation. And they can take days or weeks, depending upon how you do the scan and what the researchers were trying to accomplish.

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But the Zmap tool built by University of Michigan researchers has the ability to perform an Internet-wide scan in about 45 minutes while running on an ordinary server. The tool, which the team presented at the USENIX Security conference last week, is open-source and freely available for other researchers to use.

To demonstrate the capabilities of Zmap, the Michigan team, consisting of J. Alex Halderman, an assistant professor, and Eric Wustrow and Zakir Durumeric, both doctoral candidates, ran a scan of the entire IPv4 address space, returning results from more 34 million hosts, or what they estimate to be about 98 percent of the machines in that space.

Zmap specifically bypasses some of the speed obstacles that have slowed down some of the previous large-scale scans of the Internet. The researchers removed some of the considerations for machines on the other end of the scan, for example assuming they sit on well-provisioned networks and can handle fast probes. The result is the tool can scan more than 1,300 times faster than the Nmap scanner.

“While Nmap adapts its transmission rate to avoid saturating the source or target networks, we assume that the source network is well provisioned (unable to be saturated by the source host), and that the targets are randomly ordered and widely dispersed (so no distant network or path is likely to be saturated by the scan). Consequently, we attempt to send probes as quickly as the source’s NIC can support, skipping the TCP/IP stack and generating Ethernet frames directly. We show that Zmap can send probes at gigabit line speed from commodity hardware and entirely in user space,” the researchers said in their paper, “Zmap: Fast Internet-Wide Scanning and Its Security Implications.”

“While Nmap maintains state for each connection to track which hosts have been scanned and to handle timeouts and retransmissions, Zmap forgoes any per-connection state. Since it is intended to target random samples of the address space, Zmap can avoid storing the addresses it has already scanned or needs to scan and instead selects addresses according to a random permutation generated by a cyclic multiplicative group.”

That stateless scanning, the researchers said, allowed Zmap to get both faster response times and better coverage of the target address space. As for practical applications of the tool, the researchers already have found several. In the last year, the team ran 110 separate scans of the entire HTTPS infrastructure, finding 42 million certificates. They only found 6.9 million certificates trusted by browsers. They also found two separate sets of mis-issued SSL certificates, something that’s been a serious problem in recent years.

The Zmap team also wrote a custom probe to look for the UPnP vulnerability that HD Moore of Rapid7 discovered in January. After scanning 15.7 million devices, they found that 3.3 million were still vulnerable. That bug can suffer exploitation with a single packet.

“Given that these vulnerable devices can be infected with a single UDP packet [25], we note that these 3.4 million devices could have been infected in approximately the same length of time — much faster than network operators can reasonably respond or for patches to be applied to vulnerable hosts. Leveraging methodology similar to Zmap, it would only have taken a matter of hours from the time of disclosure to infect every publicly available vulnerable host,” the researchers said in their paper.

Click here for more information, read the white paper, and to downlowad Zmap.



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