# CVE-2026-20103: Cisco Secure Firewall ASA and FTD Remote Access SSL VPN denial of service

Source: https://junglewise.ai/threats/cve-2026-20103-cisco-secure-firewall-asa-and-ftd-remote-access-ssl-vpn-denial-of  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-04. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-20103 · Severity: high · CVSS 8.6 · Published 2026-03-04

Cisco Secure Firewall appliances (ASA and Threat Defense) used to protect enterprise networks include a remote access SSL VPN feature. A vulnerability in this VPN functionality allows unauthenticated attackers to send specially crafted packets that exhaust device memory, causing the VPN service to stop accepting new connections and rendering the appliance unable to respond to legitimate users seeking VPN access.

Technologies: [Cisco Secure Firewall Adaptive Security Appliance (ASA) Software](https://junglewise.ai/threats/technologies/secure-firewall-adaptive-security-appliance-asa-software), [Cisco Secure Firewall Threat Defense (FTD) Software](https://junglewise.ai/threats/technologies/secure-firewall-threat-defense-ftd-software). Vendors: [Cisco](https://junglewise.ai/threats/vendors/cisco).

## Quick answers

**Is CVE-2026-20103 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-20103 being exploited in the wild.

**How severe is CVE-2026-20103?** High severity, with a CVSS score of 8.6, published 4 March 2026.

**Which products and versions are affected?** Cisco Secure Firewall Adaptive Security Appliance (ASA) Software <UNKNOWN>; Cisco Secure Firewall Threat Defense (FTD) Software <UNKNOWN>.

**Is there a fix for CVE-2026-20103?** A patch was published on 2026-03-04: Software updates released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-20103 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-20103?** Check whether you run Cisco Secure Firewall Adaptive Security Appliance (ASA) Software or Cisco Secure Firewall Threat Defense (FTD) Software at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability stems from insufficient input validation in the Remote Access SSL VPN functionality of Cisco Secure Firewall ASA and Threat Defense (FTD) software. An unauthenticated, remote attacker can exploit this by sending crafted packets to the SSL VPN server, triggering memory exhaustion that results in denial of service. The attack vector is network-based with no authentication or user interaction required. A successful exploit prevents new VPN connections while potentially rendering the device web interface temporarily unresponsive, though management functions are not directly affected. Cisco has released software updates to address this vulnerability; no workarounds are available.

## Affected products

- Cisco Secure Firewall Adaptive Security Appliance (ASA) Software <UNKNOWN>
- Cisco Secure Firewall Threat Defense (FTD) Software <UNKNOWN>

## Timeline

- 2026-03-04: disclosed: CVE-2026-20103 published
- 2026-03-04: patched: Software updates released

## References

- [https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-m9sx6MbC](https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-m9sx6MbC)

## Related threats

- [Cisco Secure Firewall ASA and FTD SSL VPN denial of service](https://junglewise.ai/threats/cve-2026-76418-a-vulnerability-in-the-remote-access-ssl-vpn-service-of-cisco)
- [Cisco Secure Firewall ASA/FTD DNS over TCP denial of service](https://junglewise.ai/threats/cve-2026-20248-cisco-secure-firewall-asa-ftd-dns-over-tcp-denial-of-service)
- [Cisco Secure Firewall ASA/FTD denial of service in syslog rate limiting](https://junglewise.ai/threats/cve-2026-20154-cisco-secure-firewall-asa-ftd-denial-of-service-in-syslog-rate)
- [Cisco Secure Firewall ASA and FTD OSPF memory corruption denial of service](https://junglewise.ai/threats/cve-2026-20023-cisco-secure-firewall-asa-and-ftd-ospf-memory-corruption-denial)
- [Cisco Secure Firewall ASA and FTD SSL VPN denial of service](https://junglewise.ai/threats/cve-2026-20106-cisco-secure-firewall-asa-and-ftd-ssl-vpn-denial-of-service)