Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software TCP DNS Denial of Service Vulnerability
Summary
| CVE | CVE-2026-20248 |
|---|---|
| State | PUBLISHED |
| Assigner | cisco |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-09-16 21:17:08 UTC |
| Updated | 2026-09-18 13:28:28 UTC |
| Description | A vulnerability in the DNS over TCP implementation of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the TCP DNS response handler to unexpectedly restart, causing the device to reload. This vulnerability is due to a logic error when parsing a DNS query and tracking the size of the incoming buffers. An attacker could exploit this vulnerability by formatting a crafted reply to a DNS query sent from the targeted device. A successful exploit could allow the attacker to cause the device to reload, causing a denial of service (DoS) condition. Note: The attacker must be able to respond to DNS queries from the device, either by controlling the DNS service or through a machine-in-the-middle attack. |
Risk And Classification
Primary CVSS: v3.1 6.8 MEDIUM from [email protected]
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H
EPSS: 0.003400000 probability, percentile 0.275350000 (date 2026-09-20)
Problem Types: CWE-195 | CWE-195 Signed to Unsigned Conversion Error
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 6.8 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H |
| 3.1 | CNA | CVSSV3_1 | 6.8 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
HighPrivileges Required
NoneUser Interaction
NoneScope
ChangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H
Vendor Declared Affected Products
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd... | [email protected] | sec.cloudapps.cisco.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
Additional Advisory Data
Exploits
CNA: The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
There are currently no legacy QID mappings associated with this CVE.