# CVE-2026-20039: Cisco Secure Firewall ASA and FTD VPN web server denial of service

Source: https://junglewise.ai/threats/cve-2026-20039-cisco-secure-firewall-asa-and-ftd-vpn-web-server-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-2026-20039 · Severity: high · CVSS 8.6 · Published 2026-03-04

Cisco's Secure Firewall Adaptive Security Appliance (ASA) and Threat Defense (FTD) products include a VPN web server used to manage remote access connections. A memory management defect allows an unauthenticated attacker to send crafted HTTP requests that exhaust resources and force the device to reload, causing an outage of the firewall and any VPNs it manages.

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

## Quick answers

**Is CVE-2026-20039 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-20039 being exploited in the wild.

**How severe is CVE-2026-20039?** 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) <UNKNOWN>; Cisco Secure Firewall Threat Defense (FTD) <UNKNOWN>.

**Is there a fix for CVE-2026-20039?** 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-2026-20039 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-20039?** Check whether you run Cisco Secure Firewall Adaptive Security Appliance (Asa) or Cisco Secure Firewall Threat Defense (FTD) 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

This vulnerability is a denial of service flaw caused by ineffective memory management in the VPN web server component (CWE-244). The vulnerability affects devices with IKEv2 Remote Access VPN with client services or SSL VPN configured. An unauthenticated remote attacker can exploit this by sending a large number of crafted HTTP requests to the affected device's web server; no authentication or special privileges are required. A successful exploit causes the device to reload, resulting in a denial of service condition. Cisco has released fixed software versions to address this issue; no workarounds are available.

## Affected products

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

## Timeline

- 2026-03-04: disclosed

## References

- [https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-dos-SpOFF2Re](https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-vpn-dos-SpOFF2Re)

## Related threats

- [Cisco Secure Firewall ASA and FTD EIGRP denial of service](https://junglewise.ai/threats/cve-2026-20222-cisco-secure-firewall-asa-and-ftd-eigrp-denial-of-service)
- [Cisco Secure Firewall Threat Defense TLS 1.3 denial of service](https://junglewise.ai/threats/cve-2026-20135-cisco-secure-firewall-threat-defense-tls-1-3-denial-of-service)
- [Cisco Snort 3 detection engine denial of service](https://junglewise.ai/threats/cve-2026-20067-cisco-snort-3-detection-engine-denial-of-service)
- [Cisco Snort 3 VBA decompression denial of service](https://junglewise.ai/threats/cve-2026-20058-cisco-snort-3-vba-decompression-denial-of-service)
- [Cisco Snort 3 VBA decompression denial of service](https://junglewise.ai/threats/cve-2026-20054-cisco-snort-3-vba-decompression-denial-of-service)