The vulnerability CVE-2020-27124 was discovered in the SSL/TLS handler of Cisco Adaptive Security Appliance (ASA) Software, a widely used security solution. This vulnerability can allow an unauthenticated, remote attacker to cause the affected device to reload unexpectedly, resulting in a denial of service (DoS) condition. In this long read, we will delve into the details of this exploit, the code snippet, original references, and the steps that Cisco has taken to mitigate this issue.

Vulnerability Explained

The vulnerability is a result of improper error handling on established SSL/TLS connections. A remote attacker can exploit this vulnerability by establishing an SSL/TLS connection with the affected device, and then sending a malicious SSL/TLS message within that connection. If the attack is successful, this will result in the device being reloaded, causing a DoS condition.

Below is a simple, high-level example of how an attacker might exploit this vulnerability

import socket
import ssl

target_host = "192.168..1" # IP address of the affected device
target_port = 443 # SSL/TLS port

# Establish a TCP connection
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_host, target_port))

# Establish an SSL/TLS connection
ssl_sock = ssl.wrap_socket(sock)

# Send malicious SSL/TLS message to exploit the vulnerability
malicious_message = "MALICIOUS_SSL/TLS_MESSAGE_HERE"
ssl_sock.sendall(malicious_message.encode('utf-8'))

ssl_sock.close()

Please note that this is only a high-level example and not an actual exploit code. The purpose of providing the snippet is to help understand how the vulnerability can be potentially exploited.

Original References

Cisco has published an official security advisory detailing this vulnerability and the mitigation steps taken. You can view the complete advisory at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-tls-rSnvu5GQ

Exploit Details

According to Cisco, this vulnerability affects Cisco ASA Software running on the following Cisco products:

FTD Virtual (FTDv)

Cisco has assigned a CVSS (Common Vulnerability Scoring System) score of 8.6 out of 10 to this vulnerability, indicating a high level of severity.

Mitigation

Cisco has released software updates that address this vulnerability. Users are advised to update their Cisco ASA Software to the latest version to protect their networks from this vulnerability. Detailed information about the security fixes and the updated versions can be found in the security advisory mentioned above.

Currently, there are no workarounds that specifically address this vulnerability.

Conclusion

CVE-2020-27124 is a critical vulnerability that may result in a DoS condition for devices running Cisco ASA Software. The vulnerability lies in the improper error handling of SSL/TLS connections, and an attacker can exploit it by sending a malicious SSL/TLS message after establishing a connection. It's essential for users to update their Cisco ASA Software to the latest version to protect their devices from potential exploits.

Timeline

Published on: 11/18/2024 16:15:06 UTC
Last modified on: 11/18/2024 17:11:17 UTC