CVE-2018-0158: Cisco IOS and XE Software Internet Key Exchange Memory Leak Vulnerability

CVE-2018-0158 is a denial-of-service vulnerability in the Internet Key Exchange Version 1 (IKEv1) implementation in Cisco IOS Software and Cisco IOS XE Software. An unauthenticated remote attacker can trigger it to force an affected device to reload, disrupting network availability.

For IT and security teams running Cisco routers or switches that terminate IPsec or related VPN traffic, this matters because a simple remote condition can take critical infrastructure offline until it recovers. Confirm all version and configuration details against the vendor advisory before acting.

How it works

The underlying weakness is classified as CWE-20 (Improper Input Validation). In this case it manifests as a memory leak within the IKEv1 handling code of Cisco IOS and IOS XE.

An attacker who can reach the IKEv1 service on an affected device sends crafted packets that the software fails to process cleanly. Over time the leak exhausts resources until the device reloads, producing a denial-of-service condition. No authentication is required. Exact packet formats and trigger conditions are not detailed here; treat any publicly reachable IKEv1 endpoint as potentially exposed and verify behavior against the Cisco advisory.

Am I affected? How to find it in your systems

Cisco IOS and IOS XE commonly run on enterprise and service-provider routers, switches, and security appliances that terminate site-to-site or remote-access VPNs. Inventory every device that has IKEv1 enabled or that listens on the standard IKE ports.

• Collect the exact software version and feature set from each device (show version and related commands) and compare it with the fixed releases listed in the Cisco advisory for CVE-2018-0158.
• Identify configurations that enable IKEv1 or IPsec; devices that never process IKEv1 traffic are lower risk but should still be checked.
• Review interface ACLs, control-plane policing, and management-plane protections to see whether untrusted networks can reach the IKE service.
• Watch device logs and SNMP/telemetry for unexpected reloads, memory-growth trends on the IKE process, or repeated IKEv1 negotiation failures that coincide with traffic from untrusted sources. These signs are suggestive only; confirm exploitation indicators with vendor guidance.

How to remediate

Patch first. Apply the Cisco software updates identified in the vendor advisory for CVE-2018-0158, following Cisco’s published installation and verification procedures. CISA’s required action is simply to apply updates per vendor instructions.

After patching, harden the IKEv1 attack surface:

• Disable IKEv1 entirely if the environment can migrate to IKEv2 or does not require IKE.
• Restrict IKEv1 to known peer addresses with infrastructure ACLs or control-plane policing.
• Enable and tune memory and process monitoring so that gradual leaks are visible before a reload occurs.
• Re-validate VPN configurations and certificates after the upgrade to ensure no unintended exposure was introduced.

If you can't patch immediately

Reduce exposure until the vendor update can be installed:

• Segment devices so that IKEv1 is reachable only from trusted peer networks; block the service at the edge from the public Internet wherever possible.
• Apply temporary infrastructure ACLs or firewall rules that limit source addresses and rate-limit IKE traffic.
• If a virtual-patching or IDS/IPS capability exists in your environment, enable any vendor-supplied signatures for this CVE after confirming they match the advisory.
• Increase monitoring for reload events, memory exhaustion, and anomalous IKE session attempts; alert on thresholds that precede a crash.
• Document the compensating controls and schedule the permanent patch as a high-priority change.

If your data may have been exposed

This vulnerability produces a denial-of-service condition rather than direct data exfiltration, and ransomware use is not documented. Nevertheless, any actively exploited remote flaw can be a stepping-stone in a larger intrusion. If you suspect compromise, follow your incident-response process, preserve logs, and examine adjacent systems. You can also run a free exposure scan of your email addresses against known breach data sets to check whether credentials or personal information have appeared in prior incidents.