CVE-2018-0174

Cisco IOS Software and Cisco IOS XE Software contain an improper input validation flaw (CWE-20) in the DHCP option 82 encapsulation functionality. An unauthenticated remote attacker can trigger it by sending a crafted DHCPv4 packet carrying option 82 information to a device that processes packets received from DHCP relay agents. A successful exploit causes the affected device to reload, producing a denial of service; the CVSS vector confirms no confidentiality or integrity impact. Any organization running Cisco IOS or IOS XE devices that act as DHCP relay agents or otherwise handle relayed DHCP traffic is potentially affected. The flaw is in CISA's Known Exploited Vulnerabilities catalog (added 2022-03-03), indicating observed exploitation, though no public proof-of-concept is known.

What to do: Apply updated Cisco IOS/IOS XE releases per Cisco's advisory for Bug ID CSCuh91645, prioritizing devices configured as DHCP relay agents or exposed to untrusted DHCP traffic. As an interim mitigation, disable or restrict option 82 processing/insertion on relay configurations and limit DHCPv4 traffic to trusted relay agents. Verify exposure by auditing IOS/IOS XE devices for DHCP relay configurations and for receipt of relayed DHCP packets.