Description

Secure Sockets Layer (SSL) policies determine what Transport Layer Security (TLS) features clients are permitted to use when connecting to load balancers. To prevent the use of insecure features, SSL policies should use at least TLS 1.2 with the MODERN profile, the RESTRICTED profile (which effectively requires TLS 1.2 regardless of the chosen minimum TLS version), or 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

Rationale

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 support older clients, GCP load balancers can be configured to permit insecure cipher suites. 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 As a result, it is easy to configure a load balancer without realizing that outdated cipher suites are permitted.

Impact

Creating more secure SSL policies can prevent clients using older TLS versions from establishing a connection.

Audit

From Google Cloud Console

See all load balancers by visiting https://console.cloud.google.com/net-services/loadbalancing/loadBalancers/list.
For each load balancer for SSL (Proxy) or HTTPS, click on its name to go the Load balancer details page.
Ensure that each target proxy entry in the Frontend table has an SSL Policy configured.
Click on each SSL policy to go to its SSL policy details page.
Ensure that the SSL policy satisfies one of the following conditions:
- has a Min TLS set to TLS 1.2 and Profile set to Modern profile, or
- has Profile set to Restricted. Note that a Restricted profile effectively requires clients to use TLS 1.2 regardless of the chosen minimum TLS version, or
- has Profile set to Custom and the following features are all 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 Google Cloud CLI

List all TargetHttpsProxies and TargetSslProxies.

gcloud compute target-https-proxies list
gcloud compute target-ssl-proxies list

For each target proxy, list its properties:

gcloud compute target-https-proxies describe {{target-https-proxy-name}}
gcloud compute target-ssl-proxies describe {{target-ssl-proxy-name}}

Ensure that the sslPolicy field is present and identifies the name of the SSL policy:

sslPolicy: https://www.googleapis.com/compute/v1/projects/{{project-id}}/global/sslPolicies/{{ssl-policy-name}}

If the sslPolicy field is missing from the configuration, it means that the GCP default policy is used, which is insecure.

Describe the SSL policy:

gcloud compute ssl-policies describe {{ssl-policy-name}}

Ensure that the policy satisfies one of the following conditions:
- has Profile set to Modern and minTlsVersion set to TLS_1_2, or
- has Profile set to Restricted, or
- has Profile set to Custom and enabledFeatures does not contain any of the following values:
```
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
```

Default Value

The GCP default SSL policy is the least secure setting: minimum TLS 1.0 and the Compatible profile.

Rationale​

Impact​

Audit​

From Google Cloud Console​

From Google Cloud CLI​

Default Value​

References​