# CVE-2026-20100: Cisco Secure Firewall ASA and FTD Remote Access SSL VPN denial of service

Source: https://junglewise.ai/threats/cve-2026-20100-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-2026-20100 · Severity: high · CVSS 7.7 · Published 2026-03-04

Cisco's Secure Firewall ASA and FTD devices protect corporate networks by acting as firewalls and threat defense appliances. A vulnerability in the Remote Access SSL VPN feature could allow authenticated attackers to crash these devices, causing a complete denial of service until manual reboot. This impacts organizations relying on VPN access for remote work and business continuity.

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

## Quick answers

**Is CVE-2026-20100 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-20100 being exploited in the wild.

**How severe is CVE-2026-20100?** High severity, with a CVSS score of 7.7, published 4 March 2026.

**Which products and versions are affected?** Cisco Secure Firewall Adaptive Security Appliance Software Multiple versions (see vendor advisory for specifics); Cisco Secure Firewall Threat Defense Software Multiple versions (see vendor advisory for specifics).

**Is there a fix for CVE-2026-20100?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-20100 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-20100?** Check whether you run Cisco Secure Firewall Adaptive Security Appliance Software or Cisco Secure Firewall Threat Defense 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 exists in the LUA interpreter component of the Remote Access SSL VPN feature, which fails to properly validate user-supplied input before processing it. An authenticated, remote attacker with a valid VPN connection can send crafted HTTP packets to exploit this flaw, triggering an unhandled condition that causes the device to reload unexpectedly. The attack vector is network-accessible and requires an authenticated VPN session. Cisco has released software patches to address this issue; no workarounds are available.

## Affected products

- Cisco Secure Firewall Adaptive Security Appliance Software Multiple versions (see vendor advisory for specifics)
- Cisco Secure Firewall Threat Defense Software Multiple versions (see vendor advisory for specifics)

## Timeline

- 2026-03-04: disclosed: Publicly disclosed by Cisco

## 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)

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- [Cisco Secure Firewall ASA and FTD DTLS denial of service](https://junglewise.ai/threats/cve-2026-20250-cisco-secure-firewall-asa-and-ftd-dtls-denial-of-service)