Improper Input Validation in Cisco IOS/IOS XE (CVE‑2018‑0173) Enables DHCPv4 Denial‑of‑Service
What It Is – Cisco IOS and IOS XE contain an input‑validation flaw in the function that restores encapsulated option 82 information in DHCPv4 packets. An attacker can craft a malicious DHCP packet that triggers the flaw and forces the device to crash or restart.
Exploitability – The vulnerability is publicly disclosed (CVE‑2018‑0173) and has an assigned CVSS 3.1 base score of 7.5 (High). No public exploit code is known, but the attack vector is straightforward: send a malformed DHCPv4 packet to a vulnerable router or switch.
Affected Products – Cisco IOS Software and Cisco IOS XE Software on devices that process DHCPv4 traffic (e.g., routers, switches, and some firewalls).
Why It Matters for Trust & Control Assurance
- Configuration integrity – The flaw highlights the need for rigorous configuration‑management controls and evidence that devices run approved, patched firmware.
- Continuous monitoring – Detecting unexpected DHCP traffic or device restarts provides audit‑ready logs that demonstrate a defensible security posture.
- Vendor‑oversight – Maintaining up‑to‑date vendor advisories and patch cycles is a core control that satisfies multiple framework objectives (e.g., NIST CSF “Protect” and ISO 27001 “Asset Management”).
Recommended Actions
- Apply Cisco’s security advisory patch or upgrade to a version where CVE‑2018‑0173 is fixed.
- Verify DHCP option 82 handling is disabled or restricted to trusted interfaces if not required.
- Enable logging of DHCP packet processing and device crash events; retain logs for at least 90 days.
- Incorporate the patch status into your continuous control‑mapping process to produce audit‑ready evidence.
Source: CISA KEV – CVE‑2018‑0173