Remote code execution vulnerabilities in the standard implementation of the network time protocol (NTP) can be exploited by attackers to compromise servers, embedded devices and even critical infrastructure systems that run UNIX-like operating systems.
The flaws, which can be exploited by sending specially crafted packets to machines running a vulnerable version of the NTP daemon (ntpd), pose a greater threat to systems where the service runs under a highly privileged user account such as root.
However, even if the ntpd user has limited privileges, attackers could leverage other privilege escalation flaws to gain root access after exploiting the NTP flaws.
The Network Time Foundation, the organization that oversees the NTP project, has released version 4.2.8 of the standard protocol implementation to address the vulnerabilities. Some Linux distributions, including Red Hat have issued updated packages based on it, but others such as Ubuntu have yet to do so. Manufacturers of network security appliances and other embedded devices are likely still evaluating whether the flaws affect their products.
According to a security notice from the Network Time Foundation, the ntp 4.2.8 update fixes four buffer overflow vulnerabilities, tracked together as CVE-2014-9295 in the Common Vulnerabilities and Exposures database, and three other weaknesses in the protocol's cryptographic implementation and error handling. All issues were discovered by Neel Mehta and Stephen Roettger of the Google Security Team.
The U.S. government's Industrial Control Systems Cyber Emergency Response Team (ICS-CERT) warned in an advisory Friday that exploit code for these vulnerabilities is publicly available already, which increases the risk associated with them. The organization advised industrial control system operators to evaluate the impact of the flaws in their respective environments, which may differ based on particular configurations.
"Ntpd typically does not have to run as root," said Johannes Ullrich, the CTO of the SANS Internet Storm Center, in a blog post. "Most Unix/Linux versions will configure NTP using a lower privileged user."
"Try to block inbound connections to ntp servers who do not have to be publicly reachable," Ullrich said. "However, be aware that simple stateful firewalls may not track UDP connections correctly and will allow access to internal NTP servers from any external IP if the NTP server recently established an outbound connection."
Systems administrators are advised the install the NTP patches as soon as they becomes available for their systems.