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major vulnerability· requires attention

Targets widely deployed Cisco Secure Firewall (ASA/FTD); can cause firewall outages and widespread network disruption.

Networks

CVE-2026-20154

8.6
High
EPSS n/aPatch availableSep 18, 2026

Unauthenticated SYN-flood triggers CPU spike on Cisco ASA/FTD causing DoS

common questions

Is CVE-2026-20154 being exploited?

Not confirmed. CVE-2026-20154 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked.

How severe is CVE-2026-20154?

CVE-2026-20154 is rated High with a CVSS score of 8.6. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2026-20154?

Yes. A fix has been recorded for CVE-2026-20154. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2026-20154 affect?

CVE-2026-20154 affects Cisco Secure Firewall Adaptive Security Appliance (ASA) Software, Cisco Secure Firewall Threat Defense (FTD) Software. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

What should I do about CVE-2026-20154?

Apply Cisco updates immediately; implement SYN flood rate-limiting and ACLs.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

executive summary
technical analysis
affected
Cisco Secure Firewall Adaptive Security Appliance (ASA) SoftwareCisco Secure Firewall Threat Defense (FTD) Software
impact

Remote unauthenticated attacker can send SYN floods that exploit improper syslog rate-limiting to cause high CPU and DoS on ASA/FTD devices.

action required

Immediate action required

affected versions
Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
  • affected9.16.1
  • affected9.16.1.28
  • affected9.16.2
  • affected9.16.2.3
  • affected9.16.2.7
  • affected9.16.2.11
  • affected9.16.2.13
  • affected9.16.2.14
  • affected9.16.3.3
  • affected9.16.3
  • affected9.16.3.14
  • affected9.18.1
  • affected9.16.3.15
  • affected9.18.1.3
  • affected9.18.2
  • affected9.16.3.19
  • affected9.16.3.23
  • affected9.18.2.5
  • affected9.16.4
  • affected9.18.2.7
  • affected9.19.1
  • affected9.16.4.9
  • affected9.18.2.8
  • affected9.16.4.14
  • affected9.18.3
  • affected9.19.1.5
  • affected9.16.4.18
  • affected9.19.1.9
  • affected9.18.3.39
  • affected9.16.4.19
  • affected9.19.1.12
  • affected9.18.3.46
  • affected9.16.4.27
  • affected9.19.1.18
  • affected9.18.3.53
  • affected9.18.3.55
  • affected9.16.4.38
  • affected9.16.4.39
  • affected9.18.3.56
  • affected9.20.1
  • affected9.16.4.42
  • affected9.19.1.22
  • affected9.18.4
  • affected9.20.1.5
  • affected9.18.4.5
  • affected9.19.1.24
  • affected9.16.4.48
  • affected9.18.4.8
  • affected9.20.2
  • affected9.19.1.27
  • affected9.16.4.55
  • affected9.18.4.22
  • affected9.20.2.10
  • affected9.16.4.57
  • affected9.19.1.28
  • affected9.18.4.24
  • affected9.20.2.21
  • affected9.16.4.61
  • affected9.19.1.31
  • affected9.18.4.29
  • affected9.20.2.22
  • affected9.16.4.62
  • affected9.18.4.34
  • affected9.20.3
  • affected9.16.4.67
  • affected9.16.4.70
  • affected9.18.4.40
  • affected9.23.1
  • affected9.22.1.1
  • affected9.16.4.71
  • affected9.20.3.4
  • affected9.18.4.47
  • affected9.20.3.7
  • affected9.19.1.37
  • affected9.16.4.76
  • affected9.20.3.9
  • affected9.19.1.38
  • affected9.18.4.50
  • affected9.22.1.3
  • affected9.20.3.10
  • affected9.22.1.2
  • affected9.18.4.52
  • affected9.20.3.13
  • affected9.22.1.6
  • affected9.18.4.53
  • affected9.16.4.82
  • affected9.22.2
  • affected9.20.3.16
  • affected9.19.1.42
  • affected9.18.4.57
  • affected9.16.4.84
  • affected9.23.1.3
  • affected9.20.3.20
  • affected9.22.2.4
  • affected9.23.1.7
  • affected9.20.4
  • affected9.22.2.9
  • affected9.23.1.13
  • affected9.20.4.7
  • affected9.22.2.13
  • affected9.18.4.66
  • affected9.20.4.10
  • affected9.23.1.19
  • affected9.16.4.85
  • affected9.22.2.14
  • affected9.18.4.67
  • affected9.18.4.68
  • affected9.23.1.22
  • affected9.20.4.14
  • affected9.22.2.20
Cisco Cisco Secure Firewall Threat Defense (FTD) Software
  • affected7.0.0
  • affected7.0.0.1
  • affected7.0.1
  • affected7.0.1.1
  • affected7.0.2
  • affected7.2.0
  • affected7.0.2.1
  • affected7.0.3
  • affected7.2.0.1
  • affected7.0.4
  • affected7.2.1
  • affected7.0.5
  • affected7.3.0
  • affected7.2.2
  • affected7.2.3
  • affected7.3.1
  • affected7.2.4
  • affected7.0.6
  • affected7.2.5
  • affected7.2.4.1
  • affected7.3.1.1
  • affected7.4.0
  • affected7.0.6.1
  • affected7.2.5.1
  • affected7.4.1
  • affected7.2.6
  • affected7.0.6.2
  • affected7.4.1.1
  • affected7.2.7
  • affected7.2.5.2
  • affected7.3.1.2
  • affected7.2.8
  • affected7.6.0
  • affected7.4.2
  • affected7.2.8.1
  • affected7.0.6.3
  • affected7.4.2.1
  • affected7.2.9
  • affected7.0.7
  • affected7.7.0
  • affected7.4.2.2
  • affected7.2.10
  • affected7.6.1
  • affected7.4.2.3
  • affected7.0.8
  • affected7.6.2
  • affected7.7.10
  • affected7.7.11
  • affected7.0.8.1
  • affected7.6.2.1
  • affected7.7.10.1
  • affected7.4.2.4
  • affected7.2.10.2
  • affected7.4.3
  • affected7.6.4
  • affected7.4.4

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

how to fix
Remediation steps are tailored for users whose stack is affected. Add this technology to your stack to see the fix checklist.
references
NVDCVE.orgCVE DetailsSource
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