Security policy overview

Google Cloud Armor security policies protect your application by providing Layer 7 filtering and by scrubbing incoming requests for common web attacks or other Layer 7 attributes to potentially block traffic before it reaches your load balanced backend services or backend buckets. Each security policy is made up of a set of rules that filter traffic based on conditions such as an incoming request's IP address, IP range, region code, or request headers.

Google Cloud Armor security policies are available only for backend services behind an external HTTP(S) load balancer. The load balancer can be in Premium Tier or Standard Tier.

The backends to the backend service can be any of the following:

When you use Google Cloud Armor to protect a hybrid deployment or a multi-cloud architecture, the backends must be internet NEGs. Google Cloud Armor also protects serverless NEGs when traffic is routed through a load balancer. To ensure that only traffic that has been routed through your load balancer reaches your serverless NEG, see Ingress controls.

Protect your Google Cloud deployments with Google Cloud Armor security policies

HTTP(S) Load Balancing is implemented at the edge of Google's network in Google's points of presence (PoPs) around the world. In Premium Tier, user traffic directed to an external HTTP(S) load balancer enters the PoP closest to the user. It is then load balanced over Google's global network to the closest backend that has sufficient capacity available. In Standard Tier, user traffic enters Google's network through peering, ISP, or transit networks in the region where you have deployed your Google Cloud resources.

Google Cloud Armor security policies enable you to allow or deny access to your external HTTP(S) load balancer at the Google Cloud edge, as close as possible to the source of incoming traffic. This prevents unwelcome traffic from consuming resources or entering your Virtual Private Cloud (VPC) networks.

The following diagram illustrates the location of the external HTTP(S) load balancers, the Google network, and Google data centers.

Google Cloud Armor policy at network edge.
Google Cloud Armor policy at network edge (click to enlarge)

Requirements

These are the requirements for using Google Cloud Armor security policies:

  • The load balancer must be an external HTTP(S) load balancer.
  • The backend service's load balancing scheme must be EXTERNAL.
  • The backend service's protocol must be one of HTTP, HTTPS, or HTTP/2.

About Google Cloud Armor security policies

Google Cloud Armor security policies are sets of rules that match on attributes from Layer 3 to Layer 7 to protect externally facing applications or services. Each rule is evaluated with respect to incoming traffic.

A Google Cloud Armor security policy rule consists of a match condition and an action to take when that condition is met. Conditions can be as simple as whether the incoming traffic's source IP address matches a specific IP address or CIDR range (also known as IP address allowlist and denylist rules). Alternatively, by using the Google Cloud Armor custom rules language reference, you can create custom conditions that match on various attributes of the incoming traffic, such as the URL path, request method, or request header values.

When an incoming request matches a condition in a security policy rule, Google Cloud Armor either allows or denies the request, based on whether the rule is an allow rule or a deny rule.

You can associate a Google Cloud Armor security policy with one or more backend services. A backend service can have only one security policy associated with it, but your backend services do not all need to be associated with the same security policy.

If a Google Cloud Armor security policy is associated with any backend service, it can't be deleted. A backend service can be deleted regardless of whether it has an associated security policy.

If multiple forwarding rules point to a backend service that has an associated security policy, the policy rules are enforced for all traffic coming in to each of the forwarding rule IP addresses.

In the following illustration, the Google Cloud Armor security policy internal-users-policy is associated with the backend service test-network.

Google Cloud Armor security policy at network edge.
Google Cloud Armor security policy at network edge (click to enlarge)

Google Cloud Armor security policies have the following core features:

  • You can optionally use the QUIC protocol with load balancers that use Google Cloud Armor.

  • You can use Google Cloud Armor with external HTTP(S) load balancers that are in either of the following Network Service Tiers:

    • Premium Tier
    • Standard Tier
  • You can use security policies with GKE and the default Ingress controller.

Types of security policies

The following table shows the types of security policies and what you can do with them. A check mark (✔) indicates that the type of security policy supports the feature.

Backend security policy Edge security policy (Preview)
Attachment point (protected resource) Backend service
  • Backend service
  • Backend bucket
Rule actions
  • Allow
  • Deny
  • Allow
  • Deny
Source IP address
Source geography
Layer 7 filtering
WAF
Adaptive protection
Named IP address lists

Backend security policies

Backend security policies are used to protect backend services exposed by an external HTTP(S) load balancer. They can be used to filter requests and protect backend services containing instance groups or network endpoint groups (NEGs) including internet, zonal, and serverless NEGs.

Edge security policies

Edge security policies enable users to configure filtering and access control policies for content that is stored in cache; this includes endpoints like Cloud CDN-enabled backend services and Cloud Storage buckets. Edge security policies support filtering based on a subset of parameters compared to backend security policies.

Edge security policies can be configured to filter requests before the request is served from Google's cache. Edge security policies are deployed and enforced at the outermost perimeter of Google's network, upstream of where the Cloud CDN cache resides. Edge security policies can coexist with backend security policies to provide two layers of protection. They can be simultaneously applied to a backend service regardless of the resources that the backend service points to (for example, instance groups or network endpoint groups). Only edge security policies can be applied to backend buckets.

Rule evaluation order

Rule evaluation order is determined by rule priority, from the lowest number to the highest number. The rule with the lowest numeric value assigned has the highest logical priority and is evaluated prior to rules with lower logical priorities. The minimum numeric priority is 0. The priority of a rule decreases as its number increases (1, 2, 3, N+1). You cannot configure two or more rules with the same priority. The priority for each rule must be set to a number from 0 to 2147483646 inclusive. The priority value 2147483647, also known as INT-MAX, is reserved for the default rule.

Priority numbers can have gaps, which enable you to add or remove rules in the future without affecting the rest of the rules. For example, 1, 2, 3, 4, 5, 9, 12, 16 is a valid series of priority numbers to which you could add rules numbered from 6 to 8, 10 to 11, and 13 to 15 in the future. You don't need to change the existing rules except for the order of execution.

Typically, the highest priority rule that matches the request is applied. However, there is an exception when HTTP POST requests are evaluated against preconfigured rules that use evaluatePreconfiguredExpr(). The exception is as follows.

For HTTP POST requests, Google Cloud Armor receives the request's header before the body (payload). Because Google Cloud Armor receives the header information first, it evaluates rules that match against the header, but it does not match any preconfigured rules on the body. If there are multiple header-based rules, Google Cloud Armor evaluates them based on their priority as expected.

After Google Cloud Armor receives the HTTP POST body, it evaluates rules that apply to both the request headers and body. As a result, it's possible that lower priority rules that allow a request's header are matched before higher priority rules that block the request's body. In such cases, it is possible that the HTTP header portion of the request is sent to the target backend service, but the POST body containing potentially malicious content is blocked.

Examples

In the following example, rules 1, 2, and 3 are evaluated in that order for the IP and HTTP header fields. However, if an IP 9.9.9.1 launches an XSS attack in the HTTP POST body, only the body is blocked (by rule 2); the HTTP header passes through to the backend (by rule 3).

Rule1
expr: inIPRange(origin.ip, '10.10.10.0/24')
action: deny(403)
priority: 1
Rule2
expr: evaluatePreconfiguredExpr('xss-stable')
action: deny(403)
priority: 2
Rule3
expr: inIPRange(origin.ip, '9.9.9.0/24')
action: allow
priority: 3
Rule-default
action: deny(403)
priority: INT-MAX

In the following example, the policy allows IP 9.9.9.1 without scanning against XSS attacks:

Rule1
expr: inIPRange(origin.ip, '10.10.10.0/24')
action: deny(403)
priority: 1
Rule2
expr: inIPRange(origin.ip, '9.9.9.0/24')
action: allow
priority: 2
Rule3
expr: evaluatePreconfiguredExpr('xss-stable')
action: deny(403)
priority: 3
Rule-default
action: allow
priority: INT-MAX

Default rule

Each Google Cloud Armor security policy contains a default rule that is matched if none of the higher priority rules are matched or if there are no other rules in the policy. The default rule is automatically assigned a priority of 2147483647 (INT-MAX), and it is always present in the security policy.

You cannot delete the default rule, but you can modify it. The default action for the default rule is allow, but you can change the action to deny.

Fingerprint

Each Google Cloud Armor security policy has a field fingerprint. The fingerprint is a hash of the contents stored in the policy. When you create a new policy, do not provide the value of this field. If you provide a value, it is ignored. However, when you update a security policy, you must specify the current fingerprint, which you get when you export or describe the policy (using EXPORT or DESCRIBE, respectively).

The fingerprint protects you from overriding another user's update. If the fingerprint that you provide is out of date, it means that the security policy was updated since you last retrieved the fingerprint. To check for any differences and to retrieve the latest fingerprint, run the DESCRIBE command.

Rules language and enforcement engine

The rules language and enforcement engine provides the following:

  • The ability to write custom rule expressions that can match on various Layer 3 through Layer 7 attributes of incoming requests. Google Cloud Armor provides a flexible language for writing custom match conditions.

  • The ability to combine multiple subexpressions in a single rule.

  • The ability to deny or allow requests based on the incoming request's region code. The region codes are based on the ISO 3166-1 alpha 2 codes. The region codes sometimes correspond to specific countries, but some encompass a country plus its associated areas. For example, the US code includes all states of the United States, one district, and six outlying areas.

Types of rules

IP address allowlist and denylist rules

You can create IP address allowlist and denylist rules within a security policy. Some examples include the following:

  • Denylisting for IP address/CIDR enables you to block a source IP address or CIDR range from accessing external HTTP(S) load balancers.

  • Allowlisting for IP address/CIDR enables you to allow a source IP address or CIDR range to access external HTTP(S) load balancers.

  • IPv4 and IPv6 addresses are supported in allowlist and denylist rules.

  • IP address rules can block or allow individual source IP addresses or CIDRs. Both IPv4 and IPv6 source addresses are supported, but IPv6 addresses must have subnet masks no larger than /64.

  • Deny rules can return an HTTP 403 (Unauthorized), 404 (Access Denied), or 502 (Bad Gateway) response.

Preconfigured rules for XSS, SQLi, LFI, RFI, and RCE

You can use preconfigured rules to mitigate the following attacks:

  • Cross-site scripting (XSS)
  • SQL injection (SQLi) attacks
  • Local file inclusion (LFI) attacks
  • Remote file inclusion (RFI) attacks
  • Remote code execution (RCE) attacks

These rules are based on the OWASP Modsecurity core rule set version 3.0.2.

Preconfigured rules for named IP address lists

Preconfigured rules for named IP address lists provide the following:

  • Integrate third-party providers' named IP address lists with Google Cloud Armor.

  • Simplify maintenance of allowed or denied IP address ranges.

  • Synchronize third-party providers' lists daily.

  • Increase your capacity for configuring IP addresses and ranges in security policies because named IP address lists are not subject to limits on the number of IP addresses per rule.

Preview mode

You can preview the effects of a rule without enforcing it. In preview mode, actions are noted in Cloud Monitoring. You can choose to preview individual rules in a security policy, or you can preview every rule in the policy.

You can enable preview mode for a rule by using the gcloud command-line tool and the --preview flag of gcloud compute security-policies rules update.

To disable preview mode, use the --no-preview flag, which is not currently documented. You can also use the Cloud Console.

Logging

Google Cloud Armor has extensive logging and lets you define how verbose your logging is. For complete information about logging, see Using request logging.

JSON parsing and verbose logging

By default, Google Cloud Armor does not parse the JSON content of POST bodies when preconfigured WAF rules are evaluated. This can cause the WAF rules to be noisy and potentially generate false positive matches on incoming requests if the protected workloads serve REST APIs or otherwise receive requests with JSON in the POST Body (Content-Type = "application/json").

A noisy rule is triggered by requests that you would most likely consider to be false positives. For example, a JSON request body such as '{"test": "123"}' triggers the SQL injection rule owasp-crs-v030001-id942431-sqli if JSON parsing is not enabled.

We recommend that you enable JSON parsing if you expect your workload to receive requests with Content-Type = "application/json"—for example, if you are serving REST APIs.

To reduce the noise and false positives, you can configure Google Cloud Armor to parse the JSON content of POST bodies. This means that Google Cloud Armor ignores structural characters of the JSON message in the POST body and looks only at the end-user-provided values in the JSON message. For more information about preconfigured WAF rules, see Tuning Google Cloud Armor WAF rules.

Additionally, you might not be able to tell why a preconfigured WAF rule was triggered by a particular request. Google Cloud Armor's default event logs contain the rule that was triggered, as well as the subsignature. However, you might need to identify the details from the incoming request that triggered the rule for troubleshooting, rule validation, or rule tuning purposes.

You can adjust the level of detail recorded in your logs. We recommend that you enable verbose logging only when you first create a policy, make changes to a policy, or troubleshoot a policy. If you enable verbose logging, it is in effect for rules in preview mode as well as active (non-previewed) rules during standard operations.

For more information about verbose logging, see Using request logging.

HTTP(S) Load Balancing request logging

Each HTTP(S) request that is evaluated against a Google Cloud Armor security policy is logged through Cloud Logging. The logs provide details such as the name of the applied security policy, the matching rule, and whether the rule was enforced. Request logging for new backend service resources is disabled by default. To ensure that Google Cloud Armor requests are logged, you must enable HTTP(S) logging for each backend service protected by a security policy.

For more information, see HTTP(S) Load Balancing logging and monitoring and Using request logging.

To view Google Cloud Armor logs, see Viewing logs.

Limitations

  • An IP address denylist/allowlist for HTTP(S) Load Balancing is not supported for Cloud Storage backend buckets.

  • Backend security policies are enforced only for cache miss requests that have passed edge security policies.

How WebSocket connections are handled

External HTTP(S) Load Balancing has built-in support for the WebSocket protocol. WebSocket channels are initiated from HTTP(S) requests. Google Cloud Armor can block a WebSocket channel from being established, for example, if an IP address denylist blocks the originating IP address. However, subsequent transactions in the channel do not conform to the HTTP protocol, and Google Cloud Armor does not evaluate any messages after the first request.

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