CVE-2026-20135 Cisco Secure Firewall Threat Defense - Denial of Service

Cisco Secure Firewall Threat Defense Software contains a denial of service vulnerability caused by improper buffer management in TLS 1.3 implementation, letting unauthenticated remote attackers crash the LINA process and reload the device, exploit requires sending crafted TLS 1.3 packets.

CVSS base score 8.6 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
EPSS
0.46% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Denial of Service
Impact
Denial Of Service
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Published
16 September 2026
Updated
15 October 2026
Weakness
CWE-415

Vendor fix

Update to the latest version of Cisco Secure Firewall Threat Defense Software.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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