CVE-2017-12240: Cisco IOS and IOS XE Software DHCP Remote Code Execution Vulnerability

Critical severity, CVSS 9.8. Actively exploited: in CISA KEV since 2022-03-03. EPSS: 13.8% chance of exploitation in the next 30 days.

The DHCP relay subsystem of Cisco IOS 12.2 through 15.6 and Cisco IOS XE Software contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary code and gain full control of an affected system. The attacker could also cause an affected system to reload, resulting in a denial of service (DoS) condition. The vulnerability is due to a buffer overflow condition in the DHCP relay subsystem of the affected software. An attacker could exploit this vulnerability by sending a crafted DHCP Version 4 (DHCPv4) packet to an affected system. A successful exploit could allow the attacker to execute arbitrary code and gain full control of the affected system or cause the affected system to reload, resulting in a DoS condition. Cisco Bug IDs: CSCsm45390, CSCuw77959.

Affected products

• Cisco IOS: from 12.2, up to and including 15.6

Published 2017-09-29. Last modified 2026-06-17.