CVE-2014-9294: Weak RNG Seed in NTP Keygen Leaves Cryptographic Protection Mechanisms Vulnerable to Brute-Force Attacks

A vulnerability (CVE-2014-9294) has been identified in the Network Time Protocol (NTP) before version 4.2.7p230, which stems from the weak utilization of a random number generator (RNG) seed in the ntp-keygen program. This makes it significantly easier for remote attackers to defeat cryptographic protection mechanisms via a brute-force attack.

Background

The Network Time Protocol (NTP) is a protocol designed to synchronize the clocks of computers across a network. It is widely used to ensure accurate timekeeping on the internet. NTP utilizes the User Datagram Protocol (UDP) as its transport mechanism. To maintain clock synchronization, computers running NTP use this transport layer to exchange timestamped packets. Cryptographic authentication is put in place to ensure the security and integrity of these timestamped packets.

The Vulnerability

The issue lies in the use of a weak RNG seed in the util/ntp-keygen.c file of the ntp-keygen program in NTP before 4.2.7p230. Remote attackers can exploit this vulnerability to defeat cryptographic protection mechanisms via a brute-force attack. The weak RNG seed can result in predictable keying material, thus compromising the security of the cryptographic authentication process.

Exploit Details

An attacker who is able to predict the NTP keys generated by ntp-keygen can potentially impersonate a legitimate NTP server, forge false NTP packets, and manipulate the victim's system time. This, in turn, could lead to various problems, such as inaccurate timestamps on sensitive files, faulty log records, denial of service, or more severe repercussions, which depend on the overall infrastructure linked to NTP.

Original References

- NTP Security Notice
- NVD - CVE-2014-9294
- CVE - CVE-2014-9294

The following code snippet from util/ntp-keygen.c shows the weak RNG seed in action

/* Initialize a random number generator */
void init_rand(void) {
    time_t now;

    /* Get current time and use as seed for RNG */
    time(&now);
    srand((unsigned int)now);
}

As can be seen, the RNG seed is initialized with the current system time, which is usually very predictable and hence makes it susceptible to brute-force attacks.

Mitigation

The vulnerability has been fixed in NTP version 4.2.7p230, and it is recommended that users upgrade their NTP installation to this or a more recent version. The NTP Project also advises users to replace any existing keying material that might have been generated with a weak RNG seed using earlier versions.

Timeline

Published on: 12/20/2014 02:59:00 UTC
Last modified on: 11/17/2021 22:15:00 UTC