Highly exploitable, CVE-2025-20127 poses a critical security risk that could lead to severe breaches.
Status: Analyzed
Last updated: 🕝 25 Aug 2025, 14:35 UTC
Originally published on: 🕔 14 Aug 2025, 17:15 UTC
Time between publication and last update: 10 days
CVSS Release: version 3
psirt@cisco.com
Primary
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
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 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.
The exploitability of CVE-2025-20127 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).
CVE-2025-20127 presents an accessible attack vector with minimal effort required. Restricting access controls and implementing security updates are critical to reducing exploitation risks.
A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.
Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.
Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.
Above is the CVSS Sub-score Breakdown for CVE-2025-20127, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.
Below is the Impact Analysis for CVE-2025-20127, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.
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