CVE-2017-3859 in ASR 920
Summary
by MITRE
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.
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Analysis
by VulDB Data Team • 11/14/2022
The vulnerability described in CVE-2017-3859 represents a critical format string vulnerability within the DHCP processing code of Cisco ASR 920 Series Aggregation Services Routers. This flaw specifically impacts the Zero Touch Provisioning feature, which is designed to automate router configuration and deployment processes. The vulnerability stems from improper input validation when handling DHCP packets, creating an opportunity for remote attackers to manipulate the device's behavior through crafted malicious packets. The affected software versions span from IOS XE release 3.13 through 3.18, indicating a significant timeframe of exposure for network infrastructure components. This type of vulnerability falls under CWE-134, which specifically addresses format string vulnerabilities where attacker-controlled data is used as a format string parameter, potentially leading to arbitrary code execution or system instability.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it allows unauthenticated remote attackers to force device reloads through carefully crafted DHCP packets. The attack vector is particularly concerning because it requires no authentication credentials and can be executed from remote locations. The affected devices must be actively listening on the DHCP server port to be vulnerable, though the default configuration does not enable this listening behavior, reducing the attack surface. However, organizations that have configured their devices to accept DHCP server functionality may find themselves exposed to this threat. The vulnerability's exploitation directly leads to denial of service conditions that can disrupt network operations and potentially cause cascading failures in network infrastructure. This aligns with ATT&CK technique T1499.004, which covers network disruption through denial of service attacks targeting network infrastructure components.
Cisco's identification of this issue through bug ID CSCuy56385 demonstrates the company's recognition of the severity impact on their network infrastructure products. The vulnerability's potential for causing device reboots represents a significant operational risk, particularly in mission-critical network environments where uptime is essential. The fact that this vulnerability exists within the Zero Touch Provisioning feature is particularly problematic, as this functionality is designed to streamline network deployment and management processes. Organizations relying on this automated provisioning capability could experience service interruptions during critical deployment phases, leading to operational delays and increased administrative overhead. The vulnerability's remote exploitability without authentication requirements makes it especially dangerous in environments where network segmentation is not properly implemented. Network administrators must consider the broader implications of this vulnerability when planning network security strategies and incident response procedures. The remediation approach typically involves applying Cisco's security patches and updates to affected IOS XE software versions, alongside configuration changes to disable unnecessary DHCP server functionality on network devices.