CVE-2025-20127 A vulnerability in the TLS 1.3 implementation for a specific cipher for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and

What is CVE-2025-20127?

CVE-2025-20127 is a high-severity vulnerability in Cisco Adaptive Security Appliance Software, published on 14 Aug 2025.

Official description

A vulnerability in the TLS 1.3 implementation for a specific cipher for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software for Cisco Firepower 3100 and 4200 Series devices could allow an authenticated, remote attacker to consume resources that are associated with incoming TLS 1.3 connections, which eventually could cause the device to stop accepting any new SSL/TLS or VPN requests. This vulnerability is due to the implementation of the TLS 1.3 Cipher TLS_CHACHA20_POLY1305_SHA256. An attacker could exploit this vulnerability by sending a large number of TLS 1.3 connections with the specific TLS 1.3 Cipher TLS_CHACHA20_POLY1305_SHA256. A successful exploit could allow the attacker to cause a denial of service (DoS) condition where no new incoming encrypted connections are accepted. The device must be reloaded to clear this condition. Note: These incoming TLS 1.3 connections include both data traffic and user-management traffic. After the device is in the vulnerable state, no new encrypted connections can be accepted.

Weakness: CWE-404

Which versions are affected by CVE-2025-20127?

It affects 2 products.

Products include Cisco Adaptive Security Appliance Software, Cisco Secure Firewall Threat Defense.

How do I fix CVE-2025-20127?

No fix has been published for CVE-2025-20127 yet. Limit exposure of the affected software until one is available.

Is CVE-2025-20127 being exploited?

There is no known exploitation of CVE-2025-20127 in the wild and no public exploit code.

Other vulnerabilities in Cisco Adaptive Security Appliance Software

• CVE-2025-20333 Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Exploited Critical 9.9
• CVE-2016-6366 Cisco Adaptive Security Appliance (ASA) SNMP Buffer Overflow Exploited High 8.8
• CVE-2026-20349 Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Heap Inspection Exploited High 8.6
• CVE-2024-20353 Cisco ASA and FTD Denial of Service Exploited High 8.6
• CVE-2016-6367 Cisco Adaptive Security Appliance (ASA) CLI Remote Code Execution Exploited High 7.8

All Cisco Adaptive Security Appliance Software vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-pgh5-2r5j-h8rf.