CVE-2018-0159 is an internet key exchange version 1 denial-of-service vulnerability in Cisco IOS Software and Cisco IOS XE Software. CISA added it to the Known Exploited Vulnerabilities catalogue on 3 March 2022, which means attackers have used it in real attacks.
How CVE-2018-0159 behaves in Cisco IOS and IOS XE
This vulnerability is a denial-of-service condition in the Internet Key Exchange version 1 control plane for Cisco IOS and IOS XE. In practical terms, it matters because IKE negotiation is part of how devices establish IPsec tunnels, so disruption can interfere with secure connectivity and downstream network services that depend on those tunnels.
DoS flaws in network infrastructure are especially disruptive when they target control-plane processing rather than a user-facing application. A resource-exhaustion or parser-failure condition can cause repeated retries, stalled negotiation, or device instability, which is why protocol-layer bugs can have outsized operational impact even when they do not expose data directly.
Why this vulnerability class is dangerous
IKE is a trust-establishment protocol, so failures in its handling can affect both availability and the reliability of encrypted communications. When an attacker can trigger a denial-of-service condition against a routing or VPN component, the result may be tunnel interruption, session churn, or broader service degradation across sites or remote access paths.
Because the affected software sits in network infrastructure, the blast radius is often larger than the individual device. One unstable edge device can affect multiple business services, create failover events, or force operators to spend time on recovery instead of routine change and monitoring work.
For authoritative product and vulnerability record details, readers should verify exposure in the NIST National Vulnerability Database and review the official CVE Program entry as the canonical identifier source.
How organisations check exposure and prioritise response
The first question is whether the organisation actually runs Cisco IOS or IOS XE in a role that uses IKEv1. That requires an accurate asset inventory, a view of exposed management and VPN surfaces, and confirmation of whether the affected feature is enabled on internet-reachable or partner-facing devices.
Exposure assessment should also include vendor advisories and the CISA Known Exploited Vulnerabilities catalogue, because active exploitation changes priority even when the software estate is large or complex. In this context, a vulnerability-management workflow is more useful than a purely theoretical risk review, which is why Vulnerability Management Guide is the most relevant internal navigation path for triage, prioritisation and verification.
If the device is internet-exposed, the urgency rises further because attackers do not need internal access to trigger the issue. If it is only used in segmented or partner networks, the response may still be important, but the immediate threat surface is narrower and should be evaluated with the actual topology rather than assumptions.
Remediation, detection and post-incident review
The practical response is to follow the vendor’s remediation guidance and apply the relevant fix or workaround as soon as operationally possible. When patching cannot happen immediately, organisations should reduce exposure by constraining who can reach the device, limiting unnecessary VPN or IKEv1 use, and tightening monitoring around repeated negotiation failures or abnormal device behavior.
Detection should focus on signs that the control plane is being stressed, such as repeated tunnel setup failures, unexpected reloads, service instability, or correlated connectivity complaints from multiple sites. After remediation, a review should confirm whether the device was only disrupted or whether the same exposure was used as a foothold for broader compromise, configuration changes, or persistence.
Where network edge devices are in scope, it is useful to compare the response plan with established DDoS handling patterns, since availability-driven attacks on infrastructure often require the same discipline around rate, reachability and recovery. The DDoS Protection Guide provides a useful conceptual bridge for understanding how protocol exhaustion can translate into service disruption.
Risk and Threat Considerations
This flaw matters most where the affected Cisco devices are critical VPN or routing choke points. An attacker who can trigger the denial-of-service condition may not need to steal data to cause damage, because service interruption alone can block remote access, break site-to-site connectivity, and force emergency failover or recovery work.
Failure mechanism: The vulnerable IKEv1 processing path can be driven into an unstable or exhausted state by malicious traffic, reducing availability of the device or the tunnels it supports.
Impact: Connectivity loss, degraded network resilience, and operational disruption can follow, especially when the device is an edge dependency for multiple business services.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
NIST CSF 2.0, NIST SP 800-53 Rev 5 and CIS Controls v8 set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| NIST CSF 2.0 | PR.PS-01 — Configuration Management | Secure device configuration and feature exposure are central to this network flaw. |
| DE.CM-01 — Monitoring for Anomalous Activity | Repeated negotiation failures and device instability require continuous monitoring. | |
| Recommendation — Harden exposed Cisco devices and disable unnecessary IKEv1 paths. Monitor edge devices for abnormal tunnel failures and control-plane stress. | ||
| NIST SP 800-53 Rev 5 | SC-7 — Boundary Protection | Internet-facing network boundaries shape exposure to protocol attacks on edge devices. |
| SI-4 — System Monitoring | Detection of attack symptoms depends on monitoring device behavior and logs. | |
| Recommendation — Restrict and segment inbound traffic to vulnerable network-edge services. Alert on repeated IKE failures, reloads, and service degradation. | ||
| CIS Controls v8 | CIS-12 — Network Infrastructure Management | This is a network infrastructure issue requiring hardened device management and change control. |
| Recommendation — Inventory and harden affected Cisco network infrastructure promptly. | ||
Practitioner Guidance
Why practitioners should care: Treat this as an infrastructure availability issue, not just a software bug. On network edge devices, a small protocol flaw can become a business outage if VPN reachability, failover, or remote operations depend on the affected path.
What to watch for: Prioritise devices that are internet-facing, handle partner connectivity, or sit in a high-availability pair. Those systems deserve the fastest validation because their failure is more likely to have immediate service impact.
Practitioner takeaway: Confirm exposure from the asset inventory, then align remediation with the vendor advisory and the KEV record rather than waiting for a routine patch cycle.
Related resources from NHI Mgmt Group
- CVE-2018-0154 (Cisco IOS Software Integrated Services Module for VPN Denial-of-Service)
- CVE-2017-12319 (Cisco IOS XE Software Ethernet Virtual Private Network Border Gateway Protocol Denial-of-Service)
- CVE-2025-20352 (Cisco IOS and IOS XE Software SNMP Denial of Service and Remote Code Execution)
- CVE-2018-0180 (Cisco IOS Software Denial-of-Service)
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Reviewed and updated by the NHIMG editorial team on October 17, 2026.
NHI Mgmt Group — the #1 independent authority on Non-Human Identity, IAM, and Agentic AI security. nhimg.org