CVE-2018-0154

What is the Cisco Integrated Services Module for VPN (ISM-VPN)?

The ISM-VPN is a hardware module that plugs into Cisco ISR routers to accelerate IPsec VPN encryption and decryption in dedicated silicon, offloading that work from the router's main CPU. It is used in branch-office and site-to-site VPN deployments where high-throughput encrypted tunnels are required, making it a piece of infrastructure that directly underpins an organization's WAN connectivity.

Overview

CVE-2018-0154 is a high-severity denial-of-service vulnerability in the crypto engine of the ISM-VPN module running Cisco IOS Software. An unauthenticated, remote attacker who can send specially crafted IPsec traffic to a device with an ISM-VPN module installed can trigger a condition that reloads the module, and potentially the entire router, interrupting encrypted VPN connectivity for every tunnel that device serves.

Technical Details

The issue is classified under CWE-399 (resource management errors): malformed packets processed by the crypto engine are not handled correctly, leading the module to enter an unstable state and reload. Because the crypto engine sits directly in the IPsec packet-processing path, it is reachable by any traffic arriving on a VPN-terminating interface — no authentication or established tunnel is required to trigger the flaw, only the ability to send packets to the listening interface.

Discovery

Cisco identified and fixed this issue internally, publishing it as part of the March 2018 semiannual IOS/IOS XE security advisory bundle alongside numerous related CWE-399 denial-of-service fixes.

Exploitation Context

CISA's KEV listing confirms real-world exploitation of this vulnerability. Denial-of-service bugs affecting VPN concentrator hardware are attractive to attackers seeking to disrupt an organization's WAN or remote-access connectivity, whether as a standalone disruption or as cover/distraction for other simultaneous activity elsewhere on the network.

Remediation

1. Identify Cisco ISR routers with an ISM-VPN module installed and confirm the running IOS software version.
2. Apply the Cisco-published fixed software release referenced in the corresponding security advisory.
3. Where patching must be delayed, restrict which external hosts can send traffic to VPN-terminating interfaces via infrastructure ACLs.
4. Monitor for unexpected module or router reloads that could indicate active exploitation.
5. Maintain redundant VPN paths where business continuity depends on the encrypted tunnel remaining available during patch windows.