CVE Intelligence
Medium

CVE-2026-20248 — Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software TCP DNS Denial of Service Vulnerability

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.

Published Sep 16, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: cisco

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
—
No EPSS score.
Affects
Cisco
Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and 1 more
CVSS base
6.8
Medium · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software, Cisco Cisco Secure Firewall Threat Defense (FTD) Software).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software version 9.16.4.89version 9.23.1.26version 9.20.4.235version 9.18.4.82version 9.20.4.34version 9.24.1.11version 9.23.1.32version 9.24.1.155
and 125 more version 9.20.4.30version 9.23.1.195version 9.18.4.135version 9.22.3.5version 9.20.4.28version 9.24.1.9version 9.20.4.22version 9.24.1.5version 9.22.3version 9.18.4.76version 9.22.2.32version 9.16.4.92version 9.16.1version 9.16.1.28version 9.16.2version 9.16.2.3version 9.16.2.7version 9.16.2.11version 9.16.2.13version 9.16.2.14version 9.16.3.3version 9.16.3version 9.16.3.14version 9.18.1version 9.16.3.15version 9.18.1.3version 9.18.2version 9.16.3.19version 9.16.3.23version 9.18.2.5version 9.16.4version 9.18.2.7version 9.19.1version 9.16.4.9version 9.18.2.8version 9.16.4.14version 9.18.3version 9.19.1.5version 9.16.4.18version 9.19.1.9version 9.18.3.39version 9.16.4.19version 9.19.1.12version 9.18.3.46version 9.16.4.27version 9.19.1.18version 9.18.3.53version 9.18.3.55version 9.16.4.38version 9.16.4.39version 9.18.3.56version 9.20.1version 9.16.4.42version 9.19.1.22version 9.18.4version 9.20.1.5version 9.18.4.5version 9.19.1.24version 9.16.4.48version 9.18.4.8version 9.20.2version 9.19.1.27version 9.16.4.55version 9.18.4.22version 9.20.2.10version 9.16.4.57version 9.19.1.28version 9.18.4.24version 9.20.2.21version 9.16.4.61version 9.19.1.31version 9.18.4.29version 9.20.2.22version 9.16.4.62version 9.18.4.34version 9.20.3version 9.16.4.67version 9.16.4.70version 9.18.4.40version 9.23.1version 9.22.1.1version 9.16.4.71version 9.20.3.4version 9.18.4.47version 9.20.3.7version 9.19.1.37version 9.16.4.76version 9.20.3.9version 9.19.1.38version 9.18.4.50version 9.22.1.3version 9.20.3.10version 9.22.1.2version 9.18.4.52version 9.20.3.13version 9.22.1.6version 9.18.4.53version 9.16.4.82version 9.22.2version 9.20.3.16version 9.19.1.42version 9.18.4.57version 9.16.4.84version 9.23.1.3version 9.20.3.20version 9.22.2.4version 9.23.1.7version 9.20.4version 9.22.2.9version 9.23.1.13version 9.20.4.7version 9.22.2.13version 9.18.4.66version 9.20.4.10version 9.23.1.19version 9.16.4.85version 9.22.2.14version 9.18.4.67version 9.24.1version 9.18.4.68version 9.23.1.22version 9.20.4.14version 9.22.2.20version 9.18.4.71version 9.20.4.19
Vulnerable CVE Program (cve.org) e CISA ADP
Cisco Cisco Secure Firewall Threat Defense (FTD) Software version 7.4.2.3version 7.6.1version 7.2.10version 7.4.2.2version 7.7.0version 7.0.7version 7.2.9version 7.4.2.1
and 52 more version 7.0.6.3version 7.2.8.1version 7.4.2version 7.6.0version 7.2.8version 7.4.7version 7.3.1.2version 7.0.8version 7.6.2version 7.7.10version 7.7.11version 7.0.8.1version 7.6.2.1version 7.7.10.1version 7.4.2.4version 7.2.10.2version 7.4.3version 7.6.4version 10.0.0version 7.4.4version 7.0.9version 7.2.11version 7.2.3version 7.0.0version 7.0.0.1version 7.0.1version 7.0.1.1version 7.0.2version 7.2.0version 7.0.2.1version 7.0.3version 7.2.0.1version 7.0.4version 7.2.1version 7.0.5version 7.3.0version 7.2.2version 7.2.5.2version 7.3.1version 7.2.4version 7.0.6version 7.2.5version 7.2.4.1version 7.3.1.1version 7.4.0version 7.0.6.1version 7.2.5.1version 7.4.1version 7.2.6version 7.0.6.2version 7.4.1.1version 7.2.7
Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
6.8 CVSS 3.1 Medium 2.2 4.0 psirt@cisco.com via NIST National Vulnerability Database
6.8 CVSS 3.1 Medium — — cisco via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H (score shown at the top: psirt@cisco.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-195

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · cisco/cisco secure firewall adaptive security appliance (asa) software, cisco/cisco secure firewall threat defense (ftd)
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 15, 2026
  • CVSS changed · 6.8
    Oct 15, 2026 · NIST National Vulnerability Database
  • Source status changed · → Awaiting Analysis
    Oct 15, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 15, 2026 · NIST National Vulnerability Database
  • CVE published
    Sep 16, 2026 · cisco

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

1 on the record

Elsewhere on this site

Cisco
every CVE for this vendor
CWE-195
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-20336 Cisco Secure Adaptive Security Appliance Software, Secure Firewall Threat Defense Software and Secure Firewall Management Center Software Hardening Release - Resource Lifetime Management Vulnerabilities 29d
  • CVE-2026-20335 Cisco Secure Adaptive Security Appliance Software, Secure Firewall Threat Defense Software and Secure Firewall Management Center Software Hardening Release - Incorrect Calculation Vulnerabilities 29d
  • CVE-2026-20334 Cisco Secure Adaptive Security Appliance Software, Secure Firewall Threat Defense Software and Secure Firewall Management Center Software Hardening Release - Coding Standards Vulnerabilities 29d
  • CVE-2026-20323 Cisco Secure Firewall Management Center and Secure Firewall Threat Defense Software sftunnel Unauthorized Authentication Bypass Vulnerability 29d
  • CVE-2026-20333 Cisco Secure Adaptive Security Appliance Software, Secure Firewall Threat Defense Software and Secure Firewall Management Center Software Hardening Release - Incorrect Comparison Vulnerabilities 29d
  • CVE-2026-20332 Cisco Secure Adaptive Security Appliance Software, Secure Firewall Threat Defense Software and Secure Firewall Management Center Software Hardening Release - Improper Access Control Vulnerabilities 29d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No FIRST EPSS score.
  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-20248 is "Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software TCP DNS Denial of Service Vulnerability", rated Medium. It affects Cisco Secure Firewall Adaptive Security Appliance (ASA) Software (Cisco); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 6.8 describes technical severity. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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