CVE-2022-20679: Cisco IOS XE IPSec DoS Vulnerability

CVE-2022-20679 Overview

A vulnerability in the IPSec decryption routine of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. This vulnerability is due to buffer exhaustion that occurs while traffic on a configured IPsec tunnel is being processed. An attacker could exploit this vulnerability by sending traffic to an affected device that has a maximum transmission unit (MTU) of 1800 bytes or greater.

Critical Impact

Successful exploitation causes the affected Cisco IOS XE device to reload, disrupting network connectivity and VPN services for all users relying on the device.

Affected Products

• Cisco IOS XE versions 3.15.1xbs through 3.15.2xbs
• Cisco IOS XE versions 16.8.x through 16.12.x (multiple point releases)
• Cisco IOS XE versions 17.1.x through 17.6.x (multiple point releases)

Discovery Timeline

• April 15, 2022 - CVE-2022-20679 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-20679

Vulnerability Analysis

This vulnerability affects the IPSec decryption processing within Cisco IOS XE Software. When traffic traverses a configured IPsec tunnel, the decryption routine fails to properly manage buffer resources. This improper handling leads to buffer exhaustion when processing specially crafted packets, ultimately causing the device to reload.

The vulnerability is classified under CWE-20 (Improper Input Validation), indicating that the IPSec decryption routine does not adequately validate or handle certain input conditions related to packet size and MTU configurations. The attack can be executed remotely over the network, though it requires the attacker to have access to the trusted network where the affected device operates. Additionally, all network devices between the attacker and the target must support an MTU of 1800 bytes or greater, which somewhat limits the attack surface.

Root Cause

The root cause of this vulnerability lies in improper input validation within the IPSec decryption routine. The decryption process fails to properly handle buffer management when processing traffic on IPsec tunnels configured with an MTU of 1800 bytes or greater. This leads to buffer exhaustion conditions that cause the device to become unresponsive and reload.

Attack Vector

The attack vector is network-based and requires the following conditions to be met:

1. The target device must be running a vulnerable version of Cisco IOS XE Software
2. An IPsec tunnel must be configured on the device
3. The tunnel interface must have an MTU configured at 1800 bytes or greater
4. The attacker must be able to send traffic that will be processed by the IPsec decryption routine
5. All network devices between the attacker and the target must support the required MTU size

The exploitation involves sending crafted traffic to the affected device through the IPsec tunnel. When the decryption routine processes this traffic, buffer exhaustion occurs, triggering a device reload. While the attack requires network access to the trusted network segment, successful exploitation results in complete denial of service for the affected device.

Detection Methods for CVE-2022-20679

Indicators of Compromise

• Unexpected device reloads or crashes on Cisco IOS XE devices with IPsec tunnels configured
• System log entries indicating buffer exhaustion or memory allocation failures in the QFP (Quantum Flow Processor) component
• Crash dump files referencing the IPsec decryption routine or related memory management functions

Detection Strategies

• Monitor Cisco IOS XE devices for unexpected reloads, particularly those with active IPsec VPN configurations
• Review syslog messages for errors related to QFP memory exhaustion or IPsec processing failures
• Implement network traffic analysis to identify unusual traffic patterns targeting IPsec endpoints with high MTU settings
• Configure SNMP traps or alerts for device reload events on critical network infrastructure

Monitoring Recommendations

• Enable enhanced logging on IPsec-enabled interfaces to capture detailed processing information
• Configure device health monitoring to track buffer utilization and memory allocation trends
• Implement network baseline monitoring to detect anomalous traffic volumes or patterns on IPsec tunnels
• Set up automated alerting for device availability and reload events across the network infrastructure

How to Mitigate CVE-2022-20679

Immediate Actions Required

• Review the Cisco Security Advisory for complete remediation guidance
• Identify all Cisco IOS XE devices running vulnerable software versions with IPsec tunnels configured
• Prioritize patching for devices with MTU configurations of 1800 bytes or greater on tunnel interfaces
• Consider temporarily reducing MTU settings below 1800 bytes as a risk mitigation measure where operationally feasible

Patch Information

Cisco has released software updates to address this vulnerability. Administrators should consult the Cisco Security Advisory for specific fixed software releases applicable to their deployment. The advisory provides detailed information on which software versions contain the fix and the recommended upgrade paths.

Organizations should follow their standard change management procedures when applying patches, ensuring that updates are tested in a non-production environment before deployment to critical infrastructure.

Workarounds

• Reduce the MTU configuration on IPsec tunnel interfaces to below 1800 bytes where network conditions permit
• Implement access control lists (ACLs) to restrict which hosts can send traffic through IPsec tunnels
• Consider network segmentation to limit attacker access to trusted network segments where affected devices operate
• Deploy intrusion detection/prevention systems to monitor for potential exploitation attempts

# Configuration example - Reduce MTU on tunnel interface
interface Tunnel0
 ip mtu 1400
 ip tcp adjust-mss 1360