Control: 3.9 Ensure no HTTPS or SSL proxy load balancers permit SSL policies with weak cipher suites

Description

Secure Sockets Layer (SSL) policies determine what port Transport Layer Security (TLS) features clients are permitted to use when connecting to load balancers. To prevent usage of insecure features, SSL policies should use (a) at least TLS 1.2 with the MODERN profile; or (b) the RESTRICTED profile, because it effectively requires clients to use TLS 1.2 regardless of the chosen minimum TLS version; or (3) a CUSTOM profile that does not support any of the following features:

TLS_RSA_WITH_AES_128_GCM_SHA256
TLS_RSA_WITH_AES_256_GCM_SHA384
TLS_RSA_WITH_AES_128_CBC_SHA
TLS_RSA_WITH_AES_256_CBC_SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA

Load balancers are used to efficiently distribute traffic across multiple servers. Both SSL proxy and HTTPS load balancers are external load balancers, meaning they distribute traffic from the Internet to a GCP network. GCP customers can configure load balancer SSL policies with a minimum TLS version (1.0, 1.1, or 1.2) that clients can use to establish a connection, along with a profile (Compatible, Modern, Restricted, or Custom) that specifies permissible cipher suites. To comply with users using outdated protocols, GCP load balancers can be configured to permit insecure cipher suites. In fact, the GCP default SSL policy uses a minimum TLS version of 1.0 and a Compatible profile, which allows the widest range of insecure cipher suites. As a result, it is easy for customers to configure a load balancer without even knowing that they are permitting outdated cipher suites.

Remediation

If the TargetSSLProxy or TargetHttpsProxy does not have an SSL policy configured, create a new SSL policy. Otherwise, modify the existing insecure policy.

From Console

1. Login to GCP to the SSL Policies
2. Click on the name of the insecure policy to go to its SSL policy details page.
3. Check the value set in Min TLS column.
4. Click pencil icon button to edit.
5. Set Minimum TLS version to TLS 1.2.
6. Set Profile to Modern or Restricted.
7. Alternatively, if the user selects the profile Custom, make sure that the following features are disabled:

TLS_RSA_WITH_AES_128_GCM_SHA256
TLS_RSA_WITH_AES_256_GCM_SHA384
TLS_RSA_WITH_AES_128_CBC_SHA
TLS_RSA_WITH_AES_256_CBC_SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA

From Command Line

1. For each insecure SSL policy, update it to use secure cyphers:

gcloud compute ssl-policies update NAME [--profile COMPATIBLE|MODERN|RESTRICTED|CUSTOM] --min-tls-version 1.2 [--custom-features
FEATURES]

2. If the target proxy has a GCP default SSL policy, use the following command corresponding to the proxy type to update it.

gcloud compute target-ssl-proxies update TARGET_SSL_PROXY_NAME --ssl-policy SSL_POLICY_NAME

gcloud compute target-https-proxies update TARGET_HTTPS_POLICY_NAME --sslpolicy SSL_POLICY_NAME