CVE-2022-20760: Cisco Firepower Threat Defense DoS Flaw

CVE-2022-20760 Overview

A vulnerability in the DNS inspection handler of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service condition (DoS) on an affected device. This vulnerability is due to a lack of proper processing of incoming requests. An attacker could exploit this vulnerability by sending crafted DNS requests at a high rate to an affected device. A successful exploit could allow the attacker to cause the device to stop responding, resulting in a DoS condition.

Critical Impact

Unauthenticated remote attackers can cause network security appliances to become unresponsive, potentially disrupting enterprise network security posture and leaving networks unprotected.

Affected Products

• Cisco Adaptive Security Appliance (ASA) Software
• Cisco Firepower Threat Defense (FTD) Software
• Cisco Firepower Threat Defense version 7.1.0

Discovery Timeline

• 2022-05-03 - CVE-2022-20760 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-20760

Vulnerability Analysis

This vulnerability resides in the DNS inspection handler component of Cisco ASA and FTD Software. The DNS inspection feature is designed to examine DNS traffic passing through the firewall to enforce security policies and detect malicious DNS activity. However, due to improper handling of incoming DNS requests, the inspection handler fails to adequately process requests when they arrive at a high rate.

The vulnerability is classified as CWE-400 (Uncontrolled Resource Consumption), indicating that the affected software does not properly limit the allocation of resources in response to incoming DNS traffic. When an attacker sends specially crafted DNS requests at an elevated rate, the device's resources become exhausted, causing the appliance to stop responding to legitimate traffic.

This represents a significant security concern because Cisco ASA and FTD devices often serve as critical network security infrastructure, protecting enterprise environments from external threats. A successful DoS attack against these devices could leave an organization's network exposed or disrupt essential business operations.

Root Cause

The root cause of CVE-2022-20760 is improper resource management within the DNS inspection handler. The vulnerability stems from a lack of proper processing of incoming requests, specifically when handling DNS packets at high volume. The inspection handler does not implement adequate rate limiting or resource throttling mechanisms, allowing an attacker to overwhelm the device by flooding it with crafted DNS requests.

Attack Vector

The attack vector for this vulnerability is network-based and requires no authentication or user interaction. An attacker can remotely target an affected Cisco ASA or FTD device by sending a high volume of crafted DNS requests to trigger the denial of service condition. The attack does not require any special privileges and can be launched from any network location that can reach the vulnerable device.

The exploitation process involves:

1. Identifying a target Cisco ASA or FTD device with DNS inspection enabled
2. Crafting DNS requests designed to consume processing resources
3. Sending these requests at a high rate to exhaust device resources
4. Causing the device to become unresponsive to legitimate traffic

For technical exploitation details, refer to the Cisco Security Advisory.

Detection Methods for CVE-2022-20760

Indicators of Compromise

• Abnormally high volume of DNS queries targeting the ASA/FTD device
• Device CPU and memory utilization spikes during DNS processing
• Increased connection drops or timeouts for legitimate traffic
• Device syslog messages indicating resource exhaustion or processing failures
• Unresponsive firewall management interfaces during attack periods

Detection Strategies

• Monitor DNS traffic patterns for unusual request rates or malformed packets
• Implement baseline monitoring for device resource utilization (CPU, memory, connections)
• Configure alerting on sudden spikes in DNS inspection processing times
• Deploy network traffic analysis to detect DNS flooding patterns
• Review ASA/FTD syslogs for resource exhaustion warnings

Monitoring Recommendations

• Enable comprehensive logging for DNS inspection events on affected devices
• Implement SNMP monitoring for device health metrics with threshold-based alerting
• Deploy network flow analysis to track DNS traffic volumes and patterns
• Configure SentinelOne Singularity to monitor network device availability
• Establish baseline metrics for normal DNS traffic to quickly identify anomalies

How to Mitigate CVE-2022-20760

Immediate Actions Required

• Review the Cisco Security Advisory for affected version details
• Inventory all Cisco ASA and FTD devices in your environment
• Prioritize patching for devices exposed to untrusted networks
• Consider temporarily disabling DNS inspection if patching is delayed and feature is non-critical
• Implement network-level rate limiting for DNS traffic as an interim measure

Patch Information

Cisco has released security updates to address this vulnerability. Organizations should consult the Cisco Security Advisory cisco-sa-asaftd-dos-nJVAwOeq for detailed information on fixed software releases and upgrade paths. The advisory provides specific version information for both ASA Software and Firepower Threat Defense Software.

Workarounds

• Implement external rate limiting for DNS traffic before it reaches the ASA/FTD device
• Configure access control lists to restrict DNS traffic sources to trusted networks only
• Consider using upstream DNS proxies to filter traffic before reaching the firewall
• Deploy redundant firewall configurations to maintain availability during potential attacks

# Example: Configure access control to limit DNS traffic sources on ASA
# Note: Adjust network ranges based on your environment
access-list DNS_RATE_LIMIT extended permit udp <trusted_network> <netmask> any eq domain
access-list DNS_RATE_LIMIT extended deny udp any any eq domain log
access-group DNS_RATE_LIMIT in interface outside