CVE-2022-20745
📋 TL;DR
An unauthenticated remote attacker can cause a denial of service (DoS) by sending a crafted HTTPS request to Cisco ASA or FTD devices with web services interface for remote access VPN enabled. This affects Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software with vulnerable configurations.
💻 Affected Systems
- Cisco Adaptive Security Appliance (ASA) Software
- Cisco Firepower Threat Defense (FTD) Software
📦 What is this software?
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
⚠️ Risk & Real-World Impact
Worst Case
Device reloads causing complete VPN service disruption, potentially affecting all remote users and network traffic through the device.
Likely Case
Temporary service interruption requiring manual intervention or automatic reboot, disrupting VPN connectivity.
If Mitigated
Minimal impact if device is behind proper network segmentation and has redundant failover configured.
🎯 Exploit Status
Exploitation requires sending crafted HTTPS requests to the vulnerable interface. No authentication required.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Multiple fixed versions available - refer to Cisco advisory for specific versions
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asafdt-webvpn-dos-tzPSYern
Restart Required: Yes
Instructions:
1. Check current software version. 2. Download appropriate fixed version from Cisco. 3. Backup configuration. 4. Apply update following Cisco upgrade procedures. 5. Verify successful update and functionality.
🔧 Temporary Workarounds
Disable vulnerable web services interface
allDisable the web services interface for remote access VPN if not required
no webvpn
no http server enable
Restrict access to VPN interface
allImplement access control lists to restrict which IPs can access the VPN interface
access-list VPN-ACL extended permit ip [trusted-networks] any
access-group VPN-ACL in interface [vpn-interface]
🧯 If You Can't Patch
- Implement strict network segmentation to isolate VPN interfaces from untrusted networks
- Deploy intrusion prevention systems (IPS) with signatures for this vulnerability
🔍 How to Verify
Check if Vulnerable:
Check if web services interface for remote access VPN is enabled and compare software version against Cisco advisoryCheck Version:
show version | include VersionVerify Fix Applied:
Verify software version is updated to fixed version and test VPN functionality📡 Detection & Monitoring
Log Indicators:
- Unexpected device reloads
- High volume of malformed HTTPS requests to VPN interface
- WebVPN process crashes
Network Indicators:
- Spike in HTTPS traffic to VPN port (typically 443)
- Unusual patterns in VPN connection attempts
SIEM Query:
source="cisco-asa" AND (message="Device reloaded" OR message="WebVPN process failure")