CVE-2022-20745 Overview
A vulnerability in the web services interface for remote access VPN features of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. This vulnerability is due to improper input validation when parsing HTTPS requests. An attacker could exploit this vulnerability by sending a crafted HTTPS request to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.
Critical Impact
Unauthenticated remote attackers can cause affected Cisco ASA and FTD devices to reload by sending crafted HTTPS requests, disrupting critical VPN and firewall services.
Affected Products
- Cisco Adaptive Security Appliance (ASA) Software
- Cisco Firepower Threat Defense (FTD) Software
- Cisco Firepower Threat Defense version 7.1.0
Discovery Timeline
- May 3, 2022 - CVE-2022-20745 published to NVD
- November 21, 2024 - Last updated in NVD database
Technical Details for CVE-2022-20745
Vulnerability Analysis
This vulnerability affects the web services interface that supports remote access VPN functionality in Cisco ASA and FTD products. The flaw stems from how these devices process incoming HTTPS requests, where insufficient input validation allows malformed requests to trigger unexpected behavior in the parsing logic.
When the vulnerable web services interface receives a specially crafted HTTPS request, the device fails to properly sanitize or validate the input data before processing. This improper input validation (CWE-20) causes the device to enter an unstable state, ultimately forcing a system reload.
The attack can be executed remotely over the network without requiring any authentication or user interaction, making it particularly dangerous for internet-facing VPN concentrators and firewall appliances. Since these devices often serve as critical network security infrastructure, a successful denial of service attack could impact an organization's entire remote access capability and perimeter security posture.
Root Cause
The vulnerability is caused by improper input validation (CWE-20) in the HTTPS request parsing mechanism of the web services interface. When the affected device receives a malformed or specially crafted HTTPS request, the parsing function fails to adequately validate the input data, leading to a condition that causes the device to crash and reload.
Attack Vector
The attack is network-based and can be executed by unauthenticated remote attackers. The attacker needs to send a crafted HTTPS request to the web services interface of an affected Cisco ASA or FTD device. This interface is typically exposed when remote access VPN features are enabled.
The vulnerability can be exploited by crafting a malicious HTTPS request that triggers the input validation flaw in the web services interface. The attack does not require valid credentials or any user interaction, and upon successful exploitation, the affected device reloads, causing service disruption. Detailed exploitation methodology is described in the Cisco Security Advisory.
Detection Methods for CVE-2022-20745
Indicators of Compromise
- Unexpected device reloads on Cisco ASA or FTD appliances with web services interface enabled
- Abnormal HTTPS traffic patterns targeting the VPN web services interface
- Crash dump files or system logs indicating parsing errors in the web services module
- Multiple connection attempts from external sources to the HTTPS management interface
Detection Strategies
- Monitor Cisco ASA/FTD system logs for unexpected reload events and crash indicators
- Implement network intrusion detection rules to identify malformed HTTPS requests targeting web services interfaces
- Review syslog messages for web services interface errors or parsing failures
- Deploy anomaly detection for unusual HTTPS traffic volumes to VPN endpoints
Monitoring Recommendations
- Enable detailed logging on Cisco ASA/FTD devices for web services interface activity
- Configure SNMP traps or syslog alerts for device reload events
- Monitor VPN availability and implement automated alerting for service disruptions
- Review device crash logs periodically for evidence of exploitation attempts
How to Mitigate CVE-2022-20745
Immediate Actions Required
- Review the Cisco Security Advisory for detailed patch information and affected version ranges
- Upgrade Cisco ASA and FTD software to patched versions as specified in the vendor advisory
- Limit access to the web services interface to trusted networks where possible
- Implement rate limiting and access controls on external-facing VPN endpoints
Patch Information
Cisco has released software updates that address this vulnerability. Customers should consult the Cisco Security Advisory (cisco-sa-asafdt-webvpn-dos-tzPSYern) to determine the appropriate fixed software versions for their deployments. The advisory provides specific fixed release information for both ASA Software and FTD Software.
Workarounds
- There are no complete workarounds for this vulnerability; patching is the recommended solution
- Restrict access to the web services interface to trusted IP addresses using ACLs
- Consider deploying a Web Application Firewall (WAF) in front of VPN endpoints to filter malicious requests
- Monitor and alert on device reloads to enable rapid incident response
# Example: Restrict web services access to trusted networks (Cisco ASA CLI)
access-list WEBVPN_ACL extended permit tcp <trusted_network> <netmask> host <asa_interface_ip> eq https
access-list WEBVPN_ACL extended deny tcp any host <asa_interface_ip> eq https
access-group WEBVPN_ACL in interface outside
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
