CVE-2026-20103
📋 TL;DR
An unauthenticated remote attacker can send crafted packets to Cisco ASA/FTD Remote Access SSL VPN servers to exhaust device memory, causing denial of service for new VPN connections. This affects Cisco Secure Firewall ASA Software and Secure Firewall Threat Defense Software with Remote Access SSL VPN enabled. The management interface may become temporarily unresponsive but remains accessible.
💻 Affected Systems
- Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
- Cisco Secure Firewall Threat Defense (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 denial of service for all new Remote Access SSL VPN connections, potentially disrupting remote workforce access and business operations.
Likely Case
Intermittent VPN connection failures and degraded performance for remote users attempting to establish new SSL VPN sessions.
If Mitigated
Minimal impact with proper network segmentation, rate limiting, and monitoring in place to detect and block attack traffic.
🎯 Exploit Status
Exploitation requires sending crafted packets to the SSL VPN service, which is relatively straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Cisco advisory for specific fixed versions
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-m9sx6MbC
Restart Required: Yes
Instructions:
1. Review Cisco advisory for affected versions. 2. Download and apply appropriate fixed software version. 3. Reboot device after patching. 4. Verify patch application and functionality.
🔧 Temporary Workarounds
Network Access Control
allRestrict access to SSL VPN service to trusted IP addresses only
access-list VPN-ACL extended permit ip [trusted-networks] any
access-group VPN-ACL in interface outside
Rate Limiting
allImplement connection rate limiting on SSL VPN interface
policy-map global_policy
class inspection_default
set connection per-client-max [number]
🧯 If You Can't Patch
- Implement strict network segmentation to limit exposure of SSL VPN interfaces
- Deploy intrusion prevention systems (IPS) with signatures for this vulnerability
🔍 How to Verify
Check if Vulnerable:
Check ASA/FTD version against affected versions in Cisco advisory and verify SSL VPN is enabledCheck Version:
show version | include VersionVerify Fix Applied:
Verify running version matches fixed version from Cisco advisory and test SSL VPN functionality📡 Detection & Monitoring
Log Indicators:
- High memory utilization alerts
- SSL VPN connection failures
- Repeated connection attempts from single sources
Network Indicators:
- Unusual volume of SSL VPN handshake packets
- Traffic patterns indicating memory exhaustion attempts
SIEM Query:
source="asa" AND (event_type="vpn" OR event_type="memory") AND (severity="critical" OR severity="high")