CVE-2022-20715
📋 TL;DR
This vulnerability allows an unauthenticated remote attacker to cause a denial of service (DoS) by sending crafted requests to the SSL VPN features of Cisco ASA and FTD software, potentially forcing the device to restart. It affects organizations using these Cisco products with remote access VPN enabled, particularly those exposed to the internet.
💻 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 →
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
⚠️ Risk & Real-World Impact
Worst Case
The affected device restarts repeatedly, causing extended service disruption and potential network downtime for VPN users.
Likely Case
Intermittent DoS events leading to temporary loss of VPN connectivity and degraded network performance.
If Mitigated
Minimal impact if patched or workarounds applied, with possible minor performance overhead from mitigations.
🎯 Exploit Status
Exploitation involves sending crafted requests, which is relatively straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to Cisco advisory for specific fixed versions (e.g., ASA 9.16.4.28, 9.17.1.13, etc.).
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-dos-tL4uA4AA
Restart Required: Yes
Instructions:
1. Review Cisco advisory for applicable fixed versions. 2. Download and apply the patch from Cisco. 3. Restart the device as required. 4. Verify the fix using version checks.
🔧 Temporary Workarounds
Disable Remote Access VPN
allTemporarily disable remote access SSL VPN features to prevent exploitation.
no webvpn
no anyconnect enable
Restrict VPN Access
allLimit VPN access to trusted IP addresses using access control lists (ACLs).
access-list VPN-ACL permit ip trusted-ip any
apply to VPN interface
🧯 If You Can't Patch
- Implement network segmentation to isolate VPN traffic and reduce attack surface.
- Monitor logs for unusual VPN connection attempts and set up alerts for DoS patterns.
🔍 How to Verify
Check if Vulnerable:
Check the device version against vulnerable ranges listed in the Cisco advisory; if using an affected version with VPN enabled, it is vulnerable.Check Version:
show versionVerify Fix Applied:
After patching, confirm the device version is updated to a fixed version and test VPN functionality for stability.📡 Detection & Monitoring
Log Indicators:
- Log entries indicating VPN connection errors or device restarts
- Unusual spikes in VPN authentication failures
Network Indicators:
- Increased traffic to VPN ports (e.g., TCP/443) from unknown sources
- Patterns of crafted requests causing service interruptions
SIEM Query:
source="asa_logs" AND (event_type="vpn_error" OR message="DoS" OR device_restart)