Overview
This report discusses the CVE-2025-20127, a critical vulnerability affecting the Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software for Cisco Firepower 3100 and 4200 Series devices. This vulnerability, if exploited, could lead to a denial of service (DoS) condition, potentially compromising the system or leading to data leakage.
Vulnerability Summary
CVE ID: CVE-2025-20127
Severity: High (CVSS score: 7.7)
Attack Vector: Network
Privileges Required: Low
User Interaction: None
Impact: Denial of Service condition, potential system compromise, or data leakage
Affected Products
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Product | Affected Versions
Cisco Secure Firewall ASA Software | All versions prior to the patch
Cisco Secure Firewall FTD Software | All versions prior to the patch
How the Exploit Works
The vulnerability arises due to a flaw in the implementation of the TLS 1.3 Cipher TLS_CHACHA20_POLY1305_SHA256. An attacker can exploit this vulnerability by sending a large number of TLS 1.3 connections with TLS_CHACHA20_POLY1305_SHA256 cipher to the targeted device. A successful exploit could lead to a denial of service (DoS) condition where no new incoming encrypted connections are accepted. The device must be reloaded to clear this condition.
Conceptual Example Code
While the specific code that could be used to exploit this vulnerability is not provided, an attacker might use a script that looks conceptually similar to the following pseudocode:
import socket
target_IP = "target.example.com"
target_port = 443
cipher = "TLS_CHACHA20_POLY1305_SHA256"
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_IP, target_port))
for _ in range(large_number):
sock.write(cipher)
sock.close()In this pseudocode, an attacker creates a large number of TLS 1.3 connections with the vulnerable cipher to the target device, leading to a DoS condition. Note that this is a conceptual representation and the actual exploit may differ significantly.
