Cisco Exposes, Helps Patch Multiple NTP Vulnerabilities

By Sean Michael Kerner  |  Posted 2015-10-26 Print this article Print
NTP flaws

Cisco security researchers help to discover multiple vulnerabilities in the Network Time Protocol.

The Network Time Protocol (NTP) is a core element of the Internet infrastructure, quite literally helping the technology world as we know it stay on time. As such, news that multiple vulnerabilities have been found in NTP is somewhat concerning. But it's not all bad news.

The flaws in NTP weren't found first by attackers and used of in some form of malicious attack; rather, the flaws were found by security researchers actively seeking to improve security for the Internet.

Cisco's Talos research group found, reported and helped fix eight security vulnerabilities in NTP: CVE-2015-7848, CVE-2015-7849, CVE-2015-7850, CVE-2015-7851, CVE-2015-7852, CVE-2015-7853, CVE-2015-7854 and CVE-2015-7871.

CVE-2015-7871 has been dubbed "NAK to the Future" by Cisco researchers. A NAK is a negative acknowledgment message sent by the NTP protocol. The flaw could have enabled an ntpd (Network Time Protocol daemon) to be manipulated by an attacker to make arbitrary changes to system time.

"This attack leverages a logic error in ntpd's handling of certain crypto-NAK packets," Cisco warned in its advisory. "When a vulnerable ntpd receives an NTP symmetric active crypto-NAK packet, it will peer with the sender bypassing the authentication typically required to establish a peer association."

Cisco isn't the only organization looking at NTP vulnerabilities. A team of researchers at Boston University published a paper titled, "Attacking the Network Time Protocol" detailing the risks and potential attack vectors present in NTP.

"We explore the risk that network attackers can exploit unauthenticated Network Time Protocol (NTP) traffic to alter the time on client systems," the paper's abstract states.

The attacks outlined by the BU research include a traffic highjack that could serve to change the time for all of an NTP's clients. Another attack is a denial-of-service (DoS) attack that could restrict a client device's ability to get clock and time synchronization services. Cisco is now collaborating with BU on some of its NTP research.

"The results of Boston University's paper 'Attacking the Network Time Protocol' are from research conducted prior to Cisco's evaluation of ntpd and our collaboration with the university,"  Rich Johnson, research manager, vulnerability development at Cisco, told eWEEK.

Johnson noted that Cisco worked with the BU researchers through a grant proposal the researchers submitted to the Cisco Research Center.

"As part of this, we collaborated more closely on our ntpd evaluations that include sharing of technical understanding of NTP and potential weaknesses," he said.

Johnson emphasized, however, that the Cisco security researchers are the ones who found and reported the eight flaws now patched in NTP.

While the flaws in NTP have the potential to cause harm, Johnson said Cisco is not aware of any active exploitation. In addition, there are patches publicly available to fix the vulnerabilities, though Johnson said that it's still too early to know how quickly patches will be deployed.

Even though multiple NTP vulnerabilities have now been patched, it's not entirely clear at this point if there are other security risks with NTP still unresolved. A key best practice for responsible disclosure is to not publicly reveal flaws that are not being actively exploited until patches exist.

"If we were aware of any pending issues, we would not comment on them until they were resolved," Johnson said. "This is in accordance with our responsible disclosure policy."

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.


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