External risk intelligence

Cisco IOS Router Denial of Service Vulnerability.

CVE advisoryKnown Exploit

CVE-2017-12232

Cisco Integrated Services Routers Generation 2 devices running specific Cisco IOS versions are affected by a protocol vulnerability. An adjacent attacker could cause a device reload, leading to a denial of service. This impacts network availability and business operations.

2Halo Surface Signal

Denial of Service

Cisco Ios

15.0 to 15.6

External exposure likelihood

Halo Surface Signal score for CVE-2017-12232

This vulnerability requires an adjacent attacker, meaning the attacker must be on the same local network segment as the router. While routers are network devices, exploitation is restricted to those with physical or logical access to the local Ethernet broadcast domain, making direct public internet exploitation uncommon and typically prevented by standard perimeter security controls.

Horizon Alert

Summary of the vulnerability and why it matters

Cisco Integrated Services Routers Generation 2 (ISR G2) running specific Cisco IOS versions are affected by a protocol implementation vulnerability. This flaw allows an attacker to cause a device reload, leading to a denial of service. The issue stems from the misclassification of Ethernet frames. This can disrupt network operations and impact the availability of connected services.

Cisco IOS routers
Ethernet frame misclassification
Denial of service

Attack Path

How an attacker could exploit the issue

A vulnerability in Cisco IOS software could allow an attacker to cause a denial of service. This occurs when a crafted Ethernet frame is sent to an affected device. A successful attack could lead to the device reloading and becoming unavailable.

Adjacent network access required.
Attacker sends crafted frame.
Device reloads, causing outage.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability impacts Cisco Integrated Services Routers Generation 2 devices running specific Cisco IOS versions. An attacker could exploit this by sending a specially crafted Ethernet frame, potentially causing the router to reload and leading to a denial-of-service condition. This could disrupt network connectivity for organizations relying on these devices. The U.S. government has identified this as a known exploited vulnerability.

Likely attacker skill level: Moderate.
Required access or conditions: Adjacent network access.
Business risk or urgency: High.

Priority actions

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability affects Cisco Integrated Services Routers Generation 2 (ISR G2) running specific versions of Cisco IOS software. An adjacent attacker could exploit this to cause a denial of service by causing the device to reload. Organizations should prioritize identifying and mitigating exposure to this risk.

Find affected routers.
Reduce exposure or isolate risk.
Apply vendor fix, verify, and monitor.

Frequently asked questions

What are Cisco ISR G2 routers used for?

Cisco Integrated Services Routers Generation 2 (ISR G2) are network devices used for routing traffic within networks. They handle data communication and can support various network services.

How does CVE-2017-12232 create a denial of service?

CVE-2017-12232 is a weakness classified as CWE-399, specifically related to resource management. A misclassified Ethernet frame sent by an attacker can cause the router to reload, making it unavailable and leading to a denial of service.

What is required for an attacker to exploit this Cisco IOS vulnerability?

An attacker needs to be on the same local network segment, or 'adjacent', to the affected router. They must then send a specially crafted Ethernet frame to trigger the vulnerability. The vulnerability is not triggered if the Ethernet frames are correctly classified.

Who should be concerned about CVE-2017-12232?

Organizations using Cisco ISR G2 routers running specific Cisco IOS versions should be concerned. Since the exploit requires an adjacent attacker, this vulnerability is considered 'internal' and less likely to be exploited from the public internet, but still poses a risk within a local network.

What is the first step for managing this Cisco IOS vulnerability?

For those running affected Cisco IOS versions on ISR G2 routers, the initial step is to review the official Cisco Security Advisory for CVE-2017-12232. This advisory will contain specific guidance on remediation or mitigation strategies.

References

Written by Nicholas Merritt

External-surface CVE analysis and Halo Surface Signal prioritization for Halo Threat Intelligence.