CVE-2026-20135
Cisco Secure Firewall Threat Defense Software TLS 1.3 Denial of Service Vulnerability
Published Sep 16, 2026
CVSS 3.1 · 8.6 High
EPSS < 1%
KEV · Not listed
Description
A vulnerability in the TLS 1.3 implementation in Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition.
This vulnerability is due to improper buffer management during the TLS 1.3 connection. An attacker could exploit this vulnerability by sending a crafted TLS 1.3 packet to an affected system through a TLS 1.3-enabled listening socket. A successful exploit could allow the attacker to cause the LINA process to crash, which would cause the device to reload. The reload can happen before or after authentication of the connection.Note: TLS 1.3 connections include both data traffic and user-management traffic.
This vulnerability is due to improper buffer management during the TLS 1.3 connection. An attacker could exploit this vulnerability by sending a crafted TLS 1.3 packet to an affected system through a TLS 1.3-enabled listening socket. A successful exploit could allow the attacker to cause the LINA process to crash, which would cause the device to reload. The reload can happen before or after authentication of the connection.Note: TLS 1.3 connections include both data traffic and user-management traffic.
Affected Products
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CVE record
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NVD configurations
No data
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Red Hat packages
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OpenCVE enrichment
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
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| Cisco | Cisco Secure Firewall Threat Defense (FTD) Software | unknown |
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No data.
No data.
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| Cisco | Secure Firewall Threat Defense |
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Remediation
Tracking
Advisories
Metrics
No CVSS v4.0
Attack Vector Network
Attack Complexity Low
Privileges Required None
Scope Changed
Confidentiality Impact None
Integrity Impact None
Availability Impact High
User Interaction None
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.667% probability within 30 days)
Exploitation none
Automatable yes
Technical Impact partial
References
History
Sep 18, 2026 9:30 PM
First appearance in the feed. Affected vendors updated
View changes
| Type | Values Removed | Values Added |
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| First Time appeared |
Cisco
Cisco secure Firewall Threat Defense |
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| Vendors & Products |
Cisco
Cisco secure Firewall Threat Defense |
Sep 17, 2026 2:30 PM
Scoring metrics updated
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| Type | Values Removed | Values Added |
|---|---|---|
| Metrics |
ssvc
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Sep 16, 2026 8:30 PM
Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Description | A vulnerability in the TLS 1.3 implementation in Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to improper buffer management during the TLS 1.3 connection. An attacker could exploit this vulnerability by sending a crafted TLS 1.3 packet to an affected system through a TLS 1.3-enabled listening socket. A successful exploit could allow the attacker to cause the LINA process to crash, which would cause the device to reload. The reload can happen before or after authentication of the connection.Note: TLS 1.3 connections include both data traffic and user-management traffic. | |
| Title | Cisco Secure Firewall Threat Defense Software TLS 1.3 Denial of Service Vulnerability | |
| Weaknesses | CWE-415 | |
| References |
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| Metrics |
cvssV3_1
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Subscriptions
Weaknesses
