CVE-2018-0172

Cisco IOS and IOS XE Software improperly validate DHCP option 82 information received in DHCPv4 packets from DHCP relay agents, creating a heap overflow condition. An unauthenticated, remote attacker can trigger the flaw by sending a crafted DHCPv4 packet with option 82 data to an affected device. Successful exploitation causes the device to reload, resulting in a denial of service; no confidentiality or integrity impact is expected, but availability of the networking device is lost. Any Cisco IOS or IOS XE device that processes option 82 information in DHCPv4 packets is affected. The vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog (added March 3, 2022), indicating confirmed exploitation in the wild, and EPSS assigns it a ~7.8% probability of exploitation over the next 30 days.

What to do: Upgrade affected Cisco IOS and IOS XE devices to a fixed release listed in the Cisco security advisory for Bug ID CSCvg62730, per the vendor's instructions. Until patched, restrict DHCPv4 traffic to trusted DHCP relay agents and avoid exposing DHCP relay functionality to untrusted networks, and check whether DHCP relay/option 82 is enabled on exposed devices. Monitor devices for unexpected reloads as a sign of attempted exploitation.