CVE-2021-1422
📋 TL;DR
A logic error in Cisco ASA and FTD software cryptography modules allows authenticated remote attackers or unauthenticated man-in-the-middle attackers to cause a denial of service by sending malicious IPsec packets. The vulnerability triggers device crashes and forced reloads, but does not compromise encrypted data. Only Cisco ASA 9.16.1 and FTD 7.0.0 are affected.
💻 Affected Systems
- Cisco Adaptive Security Appliance (ASA)
- Cisco Firepower Threat Defense (FTD)
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Persistent DoS attacks could render critical network security devices unavailable, disrupting all traffic through firewalls and VPN gateways.
Likely Case
Intermittent device crashes causing service disruptions, connection drops, and potential network instability.
If Mitigated
Minimal impact with proper network segmentation, monitoring, and quick recovery procedures in place.
🎯 Exploit Status
Requires man-in-the-middle position or authenticated access to established IPsec connections. Exploitation requires specific packet crafting knowledge.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Cisco ASA 9.16.1.15 and later, Cisco FTD 7.0.0.1 and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ftd-ipsec-dos-TFKQbgWC
Restart Required: Yes
Instructions:
1. Download appropriate fixed software from Cisco Software Center. 2. Backup current configuration. 3. Install update following Cisco upgrade procedures. 4. Reboot device. 5. Verify version and functionality.
🔧 Temporary Workarounds
Disable IPsec VPN
allTemporarily disable IPsec VPN functionality if not required for operations
no crypto ipsec transform-set <transform-set-name>
no crypto map <map-name>
no tunnel-group <group-name> type ipsec-l2l
Implement Network Controls
allRestrict IPsec traffic to trusted sources using ACLs
access-list IPSEC-ACL extended permit udp host <trusted-peer> host <local-ip> eq isakmp
access-list IPSEC-ACL extended permit esp host <trusted-peer> host <local-ip>
access-group IPSEC-ACL in interface outside
🧯 If You Can't Patch
- Implement strict network segmentation to limit exposure of IPsec endpoints
- Deploy intrusion prevention systems to detect and block malicious IPsec traffic patterns
🔍 How to Verify
Check if Vulnerable:
Check running version: 'show version' and verify if running ASA 9.16.1 or FTD 7.0.0Check Version:
show version | include VersionVerify Fix Applied:
After update, run 'show version' to confirm version is 9.16.1.15+ (ASA) or 7.0.0.1+ (FTD)📡 Detection & Monitoring
Log Indicators:
- Unexpected device reloads
- Cryptography module errors
- IPsec connection anomalies
- System crash dumps
Network Indicators:
- Malformed IPsec packets
- Unusual IPsec traffic patterns
- Multiple connection attempts to IPsec endpoints
SIEM Query:
source="cisco-asa" AND ("reload" OR "crash" OR "crypto error")