Definition

Servers may support an SSL configuration that is considered insecure. An attacker may exploit this vulnerability to execute a man-in-the-middle (MITM) attack against the server, decrypt previously captured data, or in the case of client-initiated SSL renegotiation, cause a denial of service against the server.

SSL configurations are considered insecure if a server supports one or more of the following: 

• Client Initiated SSL renegotiation
• Insecure SSL renegotiation
• Insecure ciphers
• Insecure encryption keys
• Untrusted SSL certificates
• Insecure SSL/TLS versions
• Connections without Strict-Transport-Security set
• Connections with forward secrecy disabled

Impact Description

An attacker may take advantage of this vulnerability to intercept and decrypt communications between the client and the server. Hence, this will result in negative impacts to the confidentiality and integrity of any data associated with the user.

Risk Mitigation

TLS protocols using v1.0 and v1.1 should be replaced with the latest TLS 1.2 protocol, which is considerably more secure. PCI DSS v3.2 also requires that TLS 1.0 be disabled.

Ensure that the server uses only strong TLS ciphers that support forward secrecy with at least 112-bit keys (but preferably more) to encrypt sensitive connections. This ensures that an attacker cannot capture and decrypt session information.

More Information on SSL best practices can be found here: https://www.ssllabs.com/projects/best-practices/

An alternative is to install a one-stop installer that enables TLS 1.2 and defaults to it:

https://github.com/TheLevelUp/pos-tls-patcher

This is a very comprehensive installer that is backward compatible all the way to Windows Vista