CVE-2026-20050 is a vulnerability identified in Cisco Secure Firewall Threat Defense (FTD) Software, specifically related to the Do Not Decrypt exclusion feature within its SSL decryption functionality. The root cause is improper memory management during the inspection of TLS 1.2 encrypted traffic, which leads to improper resource shutdown or release. When an attacker sends specially crafted TLS 1.2 encrypted packets through an affected device, this flaw can trigger a denial of service condition by causing the device to reload unexpectedly. This vulnerability affects a wide range of FTD software versions from 7.0.0 through 7.7.10.1 and several intermediate releases. Notably, the issue is limited to TLS 1.2 traffic; other TLS versions are not vulnerable. The vulnerability can be exploited remotely without authentication or user interaction, increasing its risk profile. The CVSS v3.1 base score is 6.8, reflecting a medium severity with network attack vector, high attack complexity, no privileges required, no user interaction, and a scope change impacting availability but not confidentiality or integrity. No known exploits have been reported in the wild as of the publication date. The vulnerability could disrupt firewall operations, potentially impacting network security monitoring and traffic inspection capabilities.

The primary impact of CVE-2026-20050 is a denial of service condition on Cisco Secure Firewall Threat Defense devices, which can cause unexpected device reloads. This disrupts firewall availability, potentially leading to network outages or degraded security posture due to loss of traffic inspection and enforcement capabilities. Organizations relying on Cisco FTD for perimeter defense, internal segmentation, or VPN termination may experience interruptions in critical security services. Given the unauthenticated remote exploitability, attackers could target exposed firewall devices to cause repeated outages, impacting business continuity and incident response capabilities. Although confidentiality and integrity are not directly affected, the availability impact can indirectly increase risk by creating windows of opportunity for other attacks. The broad range of affected versions means many organizations worldwide could be vulnerable if not patched. The lack of known exploits in the wild reduces immediate risk but does not eliminate the threat, especially as exploit code could be developed following public disclosure.

To mitigate CVE-2026-20050, organizations should promptly identify all Cisco Secure Firewall Threat Defense devices running affected software versions. The primary mitigation is to apply Cisco's security patches or software updates that address this vulnerability once they become available. Until patches are deployed, consider disabling the Do Not Decrypt exclusion feature for TLS 1.2 traffic if feasible, to prevent triggering the improper resource release condition. Network administrators should also monitor firewall logs and device health for signs of unexpected reloads or crashes. Implementing network segmentation and limiting exposure of FTD management interfaces to untrusted networks can reduce attack surface. Additionally, deploying upstream protections such as rate limiting or TLS inspection on perimeter devices may help mitigate crafted traffic attempts. Regularly reviewing Cisco security advisories and subscribing to vendor notifications will ensure timely awareness of patches and workarounds. Finally, maintaining robust incident response plans to quickly recover from potential DoS events is recommended.