CVE-2025-20253
📋 TL;DR
An unauthenticated remote attacker can send specially crafted IKEv2 packets to Cisco networking devices, causing them to enter an infinite loop that exhausts resources and forces a reload, resulting in a denial of service. This affects Cisco IOS, IOS XE, Secure Firewall ASA, and Secure FTD Software. Any device with IKEv2 enabled is vulnerable.
💻 Affected Systems
- Cisco IOS Software
- Cisco IOS XE Software
- Cisco Secure Firewall ASA Software
- Cisco Secure FTD Software
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete network outage as critical border devices reboot repeatedly, disrupting all traffic through affected routers/firewalls.
Likely Case
Intermittent service disruptions as devices reload, causing packet loss and connectivity issues until patched.
If Mitigated
Minimal impact if devices are behind firewalls blocking IKEv2 traffic from untrusted sources or if workarounds are implemented.
🎯 Exploit Status
Attack requires only network access to IKEv2 port (UDP 500/4500) and ability to craft malicious packets.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Multiple fixed releases - consult Cisco advisory for specific versions
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ftd-ios-dos-DOESHWHy
Restart Required: Yes
Instructions:
1. Check Cisco advisory for exact fixed versions for your product. 2. Download appropriate firmware from Cisco. 3. Backup configuration. 4. Apply update following Cisco upgrade procedures. 5. Verify successful upgrade and functionality.
🔧 Temporary Workarounds
Block IKEv2 from untrusted sources
allImplement ACLs to restrict IKEv2 traffic to trusted IP addresses only
access-list IKEV2-ACL permit udp <trusted_ip> any eq 500
access-list IKEV2-ACL permit udp <trusted_ip> any eq 4500
access-list IKEV2-ACL deny udp any any eq 500
access-list IKEV2-ACL deny udp any any eq 4500
Apply ACL to appropriate interfaces
Disable IKEv2 if not required
allTurn off IKEv2 feature if not needed for VPN functionality
no crypto ikev2 enable
or remove IKEv2 configuration from crypto maps and policies
🧯 If You Can't Patch
- Implement strict network segmentation to isolate affected devices from untrusted networks
- Deploy intrusion prevention systems with signatures for IKEv2 protocol anomalies
🔍 How to Verify
Check if Vulnerable:
Check current software version against affected versions in Cisco advisoryCheck Version:
show version (IOS/IOS XE) or show version detail (ASA/FTD)Verify Fix Applied:
Verify installed version matches fixed release from Cisco advisory and test IKEv2 functionality📡 Detection & Monitoring
Log Indicators:
- Unexpected device reloads
- High CPU utilization alerts
- IKEv2 negotiation failures
- Resource exhaustion warnings
Network Indicators:
- Spike in IKEv2 traffic from single source
- Malformed IKEv2 packets
- Device becoming unresponsive on IKEv2 ports
SIEM Query:
source="cisco_firewall" AND (event_type="reload" OR event_type="high_cpu") AND protocol="ikev2"