Cisco IOS ISM-VPN Crypto Engine Remote Denial of Service Vulnerability (CVE-2018-0154)
Executive & SecOps Summary
SECOPS ASSESSMENTCisco router devices running Cisco IOS Software equipped with the Integrated Services Module for VPN (ISM-VPN).
An unauthenticated, remote attacker can cause a complete Denial of Service (DoS) condition, hanging or crashing the device by sending crafted VPN traffic.
Apply the official Cisco IOS software updates immediately and restrict unauthorized VPN traffic using Access Control Lists (ACLs).
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Administrators must upgrade to a fixed Cisco IOS Software release via the Cisco Software Central. Verify your hardware inventory and perform the upgrade using the following commands:
# Verify IOS version and ISM-VPN module presence
show version
show inventory | include ISM-VPN
# Download the patched IOS image from your TFTP server and set the boot path
copy tftp: flash:
# (Enter server IP and filename, e.g., c3900-universalk9-mz.SPA.15x.bin)
configure terminal
no boot system
boot system flash c3900-universalk9-mz.SPA.15x.bin
write memory
exit
# Reload the device to apply the patch
reload2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict incoming VPN traffic to trusted peer IP addresses only using Infrastructure Access Control Lists (ACLs) to minimize the attack surface.
# Configure ACL to permit VPN traffic only from a trusted peer IP
configure terminal
ip access-list extended LIMIT_VPN_ACCESS
permit udp host 203.0.113.50 any eq non500-isakmp
permit udp host 203.0.113.50 any eq isakmp
permit esp host 203.0.113.50 any
deny udp any any eq non500-isakmp
deny udp any any eq isakmp
deny esp any any
permit ip any any
exit
# Apply the ACL to the external interface
interface GigabitEthernet0/0
ip access-group LIMIT_VPN_ACCESS in
end
write memory3. Log Audit & IoC Verification Commands
Monitor system logs for signs of cryptographic engine failures, unexpected resets, or crash dumps.
# Search system logs for crypto engine errors or crashes
show logging | include CRYPTO|Engine|HEARTBEAT|Crash
# Check the active status and error counters of the crypto engine
show crypto engine connections activeStop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2018-0154) is a resource management and input validation flaw (CWE-399) within the cryptographic engine of the Cisco Integrated Services Module for VPN (ISM-VPN) running Cisco IOS Software. The root cause lies in the insufficient handling and validation of incoming VPN traffic by the crypto acceleration hardware and driver layer. When processing specifically malformed VPN packets, the engine fails to handle exceptions gracefully, leading to resource exhaustion or kernel-level failures.
2. Exploitation Mechanics & Attack Scenario
An unauthenticated remote attacker can exploit this vulnerability by transmitting crafted VPN protocol packets (such as IPsec/ISAKMP negotiation packets) directly to the WAN interface of the target device. Because the vulnerability is triggered during the initial packet parsing and decryption phase within the crypto engine, no authentication or user interaction is required (AV:N/AC:L/PR:N/UI:N). A single successful exploit packet can trigger an unhandled exception, causing the entire router to hang or crash, resulting in a complete denial of service.
3. Infrastructure & Business Impact
As this vulnerability is listed in the CISA KEV (Known Exploited Vulnerabilities) catalog, it represents a highly critical threat with confirmed active exploitation history. A successful attack on a core gateway router disables all Site-to-Site and Remote Access VPN tunnels, isolating branch offices, halting remote workforce operations, and severely disrupting business continuity.
Official Vendor Advisories & References
A vulnerability in the crypto engine of the Cisco Integrated Services Module for VPN (ISM-VPN) running Cisco IOS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to insufficient handling of VPN traffic by the affected device. An attacker could exploit this vulnerability by sending crafted VPN traffic to an affected device. A successful exploit could allow the attacker to cause the affected device to hang or crash, resulting in a DoS condition. Cisco Bug IDs: CSCvd39267.
Frequently Asked SecOps Questions (CVE-2018-0154)
FAQQ1. How critical is CVE-2018-0154 and is it actively exploited in the wild?
CVE-2018-0154 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 7.1%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2018-0154?
Primary impacted vendors include cisco across ios, integrated_services_module_for_vpn. Scope summary: Cisco routers running Cisco IOS Software with an active Integrated Services Module for VPN (ISM-VPN) (Cisco Bug ID: CSCvd39267).
Q3. What temporary mitigations or workarounds exist for CVE-2018-0154 before patching?
[Mitigation] Apply the official Cisco IOS software updates immediately and restrict unauthorized VPN traffic using Access Control Lists (ACLs). Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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