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CVE-2026-20135

Double free

8.6 HIGHEPSS 0.46%
  1. Published16 Sept 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeChanged
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

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Frequently asked

Is CVE-2026-20135 being actively exploited?

CVE-2026-20135 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.46%.

How severe is CVE-2026-20135?

CVE-2026-20135 has a CVSS 3.1 base score of 8.6, rated high. EPSS estimates a 0.46% probability of exploitation.

How do I fix CVE-2026-20135?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-20135 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.