CVE-2017-3859 : Exploit Details and Defense Strategies

A vulnerability in the DHCP code for the Zero Touch Provisioning feature of Cisco ASR 920 Series Aggregation Services Routers could allow an unauthenticated, remote attacker to cause an affected device to reload. The vulnerability is due to a format string vulnerability when processing a crafted DHCP packet for Zero Touch Provisioning. An attacker could exploit this vulnerability by sending a specially crafted DHCP packet to an affected device. An exploit could allow the attacker to cause the device to reload, resulting in a denial of service (DoS) condition. This vulnerability affects Cisco ASR 920 Series Aggregation Services Routers that are running an affected release of Cisco IOS XE Software (3.13 through 3.18) and are listening on the DHCP server port. By default, the devices do not listen on the DHCP server port. Cisco Bug IDs: CSCuy56385.

Understanding CVE-2017-3859

This section provides insights into the nature and impact of the CVE-2017-3859 vulnerability.

What is CVE-2017-3859?

The vulnerability in the DHCP code for the Zero Touch Provisioning feature of Cisco ASR 920 Series Aggregation Services Routers allows remote attackers to trigger a device reload by exploiting a format string vulnerability in crafted DHCP packets.

The Impact of CVE-2017-3859

The exploitation of this vulnerability could lead to a denial of service (DoS) situation as the affected device would restart, potentially disrupting network operations.

Technical Details of CVE-2017-3859

This section delves into the technical aspects of CVE-2017-3859.

Vulnerability Description

The vulnerability stems from a format string vulnerability in the DHCP code used for the Zero Touch Provisioning feature of Cisco ASR 920 Series Routers.

Affected Systems and Versions

Product: Cisco IOS XE Software for Cisco ASR 920 Series Routers
Versions: 3.13 through 3.18

Exploitation Mechanism

Attackers can exploit the vulnerability by sending a specially crafted DHCP packet to the vulnerable device.

Mitigation and Prevention

Learn how to mitigate and prevent the CVE-2017-3859 vulnerability.

Immediate Steps to Take

Ensure devices are not configured to listen on the DHCP server port by default.

Long-Term Security Practices

Regularly monitor and update network configurations to prevent unauthorized access.
Implement network segmentation to limit the impact of potential attacks.

Patching and Updates

Apply patches provided by Cisco to address the vulnerability and prevent exploitation.