CVE-2014-9295 - Explained: A deeper look at the ntpd stack-based buffer overflows vulnerability

CVE-2014-9295 is a critical security vulnerability that was discovered in the Network Time Protocol daemon (ntpd) before version 4.2.8. It allows remote attackers to execute arbitrary code via a specially crafted packet. In this post, we will take a deep dive into the vulnerability details and how it can be potentially exploited, as well as the original references and code snippets.

NTP is a widely used protocol that synchronizes computer clocks over the internet. Ntpd is the daemon responsible for synchronizing the time and is present on most Unix/Linux systems. The vulnerability, first reported in December 2014, impacts several ntpd features and mainly involves three functions: (1) the crypto_recv function when the Autokey Authentication feature is used, (2) the ctl_putdata function, and (3) the configure function.

crypto_recv function and the Autokey Authentication feature

The Autokey Authentication feature is an optional component in ntpd that allows secure symmetric key-based authentication. The crypto_recv function is responsible for handling authentication-related packets. A buffer overflow in this function occurs due to the insufficient bounds checking when copying data received in a packet, allowing arbitrary code execution.

Here's a code snippet from ntpd's crypto_recv function

void
crypto_recv(
	struct recvbuf *rbufp
	)
{
	...
	memcpy(pkt->pkt.signature, rbufp->pkt.signature, length);
	...
}

In this code snippet, 'length' is a user-controlled value from the received packet, which makes it possible to carry out a buffer overflow attack. No bounds checking is performed to make sure that 'length' is within the bounds of the receiving buffer.

ctl_putdata function

Another vulnerable ntpd function is 'ctl_putdata', which is responsible for network management operations, including requests and responses from the control interface. Insufficient bounds checking in this function leads to multiple stack-based buffer overflows, which can be exploited to execute arbitrary code.

Here's a code snippet from ntpd's ctl_putdata function

void
ctl_putdata(
	char *dp,
	unsigned int dcnt,
	int binmode
	)
{
	...
	cc -= snprintf(cp, cc + 1, "%s", ext_tags[j].value);
	...
}

In this code example, 'cc' represents the number of characters in the output that should not be exceeded. However, no proper bounds checking is done, which may result in a buffer overflow.

configure function

The configure function of ntpd is also vulnerable to buffer overflow attacks. The function processes certain requests and performs dynamic reconfiguration for ntpd. The vulnerability here resides in the handling of different ntpd commands and data received over the network.

The function in question has been patched since the vulnerability was reported, but here's an example of how the code would look without the patch:

void
configure(
	struct recvbuf *rbufp
	)
{
	...
	int len;

	len = strlen((char *)pkt->pkt.config);
	strlcpy(cp, (char *)pkt->pkt.config, len);
	...
}

In this code snippet, the vulnerable part lies in using 'strlcpy' without proper bounds checking.

Exploiting CVE-2014-9295

An attacker can exploit the multiple stack-based buffer overflow vulnerabilities by sending crafted packets to a vulnerable target system running ntpd. Successful exploitation can lead to arbitrary code execution with the privileges of the ntpd process, often running as root. This means that any device that runs a vulnerable version of the NTP daemon is at risk.

Original references

The official vulnerability report can be found at the CVE's entry page: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-9295.

The official NTP advisory can be found at the NTP Project website: http://www.ntp.org/downloads.html.

Conclusion

CVE-2014-9295 represents a critical issue in ntpd and can lead to remote arbitrary code execution via crafted packets, affecting a wide range of devices. As these vulnerabilities can have severe implications, it is crucial to keep your systems up to date with the latest security patches to avoid being a victim of such attacks.

Timeline

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