Google Cloud Armor enables you to define prioritized rules with configurable match conditions and actions in a security policy. A rule takes effect, meaning that the configured action is applied, if the rule is the highest priority rule where the incoming request's attributes match those expressed in the rule's match condition.
There are two kinds of match conditions.
- A basic match condition contains lists of IP addresses or lists of IP address ranges.
- An advanced match condition contains an expression with multiple sub-expressions to match on a variety of attributes of an incoming request.
The custom rules language is used to write the expressions in advanced match conditions for security policy rules. The Google Cloud Armor custom rules language is an extension of the Common Expression Language (CEL).
An expression requires two components:
- Attributes that can be inspected in rule expressions.
- Operations that can be performed on the attributes as part of an expression.
For example, the following expression uses the attributes
22.214.171.124/24 in the operation
inIpRange(). In this case, the expression
returns true if
origin.ip is with the
126.96.36.199/24 IP address range.
Attributes represent information from an incoming request, such as the origin IP address or the requested URL path.
|origin.ip||string||The source IP address of the request.|
|request.headers||map||A string to string map of the HTTP request headers. If a header contains multiple values, the value in this map would be a comma-separated string of all of the values of the header. The keys in this map are all lowercase. Only the first 16kb of each header value is available for inspection. Any header value over 16kb is truncated per GCLB specifications.|
|request.method||string||The HTTP request method, such as
|request.path||string||The requested HTTP URL path.|
|request.scheme||string||The HTTP URL scheme such as
|request.query||string||The HTTP URL query in the format of
|origin.region_code||string||The Unicode country code that is associated with the origin IP, such
The following reference describes the operators that you can use with attributes
k) to define rule expressions.
|x == "foo"||Returns true if x is equal to the given constant string literal.|
|x == R"fo'o"||Returns true if x is equal to the given raw string literal that does not interpret escape sequences. Raw string literals are convenient for expressing strings that themselves must use escape sequence characters.|
|x == y||Returns true if x is equal to y.|
|x != y||Returns true if x is not equal to y.|
|x + y||Returns the concatenated string xy.|
|x && y||Returns true if both x and y are true.|
|x || y||Returns true if x, y, or both are true.|
|!x||Returns true if the Boolean value x is false or returns false if the Boolean value x is true.|
|x.contains(y)||Returns true if the string x contains the substring y.|
|x.startsWith(y)||Returns true if the string x begins with the substring y.|
|x.endsWith(y)||Returns true if the string x ends with the substring y.|
|x.matches(y)||Returns true if the string x matches the specified RE2 pattern y. The RE2 pattern is compiled by using the RE2::Latin1 option that disables Unicode features.|
|inIpRange(x, y)||Returns true if the IP range x contains the IP address y.|
|x.lower()||Returns the lowercase value of the string x|
|x.upper()||Returns the uppercase value of the string x|
|x.base64Decode()||Returns the base64 decoded value of x; the characters _ - are first replaced with / + respectively. Returns "" (empty string) if x is not a valid base64 value.|
|has(m['k'])||Returns true if key 'k' is available in the map 'm'|
|m['k']||Returns the value at key k in the string-to-string map m if 'k' is available, otherwise returns an error. Recommended approach is to first check for the availability using "has(m['k'])==true".|
|int(x)||Converts the string result of 'x' to an 'int' type. It can then be used to do an integer comparison using standard arithmetic operators such as '>', '<=' etc. This works only for values that are supposed to be integers.|
For each of these expressions, the action taken depends on whether the expression is included in a deny or an allow rule.
Allow or deny access based on an IP address range in IPv4 or IPv6
The following expression matches with requests from the
188.8.131.52/24 IP address
The following expression matches with requests from the
Allow or deny traffic with a specific cookie
The following expression matches with requests that have a cookie containing
has(request.headers['cookie']) && request.headers['cookie'].contains('80=BLAH')
Allow or deny traffic with a non-empty
The following expression matches with requests that have a non-empty
has(request.headers['referer']) && request.headers['referer'] != ""
Deny traffic from a specific region
If your web application isn't available in the
AU region yet, all
requests from that region must be blocked. Use the following expression,
which matches with requests from the
AU region, in a deny rule:
origin.region_code == 'AU'
The region codes are based on the ISO 3166-1 alpha
codes. In some cases, a region corresponds to a country, but this is not always
the case. For example, the
US code includes all states of the United States,
one district, and six outlying areas.
To include multiple conditions in a single rule, combine multiple
sub-expressions. In the following example, requests from
184.108.40.206/24 (such as
your alpha testers) in the
AU region match the following expression:
origin.region_code == "AU" && inIpRange(origin.ip, '220.127.116.11/24')
The following expression matches requests from
18.104.22.168 where a user
agent contains the string
inIpRange(origin.ip, '22.214.171.124/32') && has(request.headers['user-agent']) && request.headers['user-agent'].contains('WordPress')
Allow or deny traffic for a request URI that matches a regular expression
The following expression matches with requests that contain the string
bad_path in the URI:
Allow or deny traffic that contains a specific Base64 decoded value
The following expression matches with requests that have a Base64 decoded value
myValue for the
has(request.headers['user-id']) && request.headers['user-id'].base64Decode().contains('myValue')
Allow or deny traffic that has zero Content-Length in the HTTP body.
The following expression matches requests that have a zero Content-Length in the HTTP body.
int(request.headers["content-length"]) == 0
Preconfigured rules use preconfigured static signatures, regular expressions, or
both to match on HTTP request headers and query parameters. The available
preconfigured rules are based on the
OWASP Modsecurity core rule set
version 3.0.1. Cloud Armor provides two predefined expression sets:
to defend against cross-site scripting attacks, and
sqli-<version>, to defend
against SQL injection attacks. To list all of the available preconfigured rules,
see Listing the available preconfigured rules.
For more information about preconfigured rules, see the use case for preconfigured rules in the Google Cloud Armor security policy concepts document.
Expression set names
Expression set names have the format
<attack category>-<version field>. The
attack category specifies the type of attacks that you want to protect against,
xss (cross-site scripting) or
sqli (SQL injection).
The supported version fields are 'stable' and 'canary'. Additions and modifications to the rules are released in the 'canary' version first. When additions and modifications are considered safe and stable, they are promoted to the 'stable' version.
Expression set member IDs
An expression set contains several expressions, each with its own core rule set
(CRS) ID. For example, the expression set
xss-stable includes an expression
owasp-crs-v020901-id981136-xss, which corresponds to rule ID
version 2.9.1. You can use the CRS IDs to exclude specific expressions from
being used, which is useful if a particular expression consistently triggers a
false positive. For more information, see the false
For full information about the core rule set and tuning at different sensitivity levels, see Tuning Google Cloud Armor WAF rules.
Operator for preconfigured rules
|evaluatePreconfiguredExpr(string, LIST)||Returns true if any one of the expressions inside the specified
expression set returns true.
The first argument is the name of expression set, such as 'xss-stable'. The second argument (optional) is a comma separated string list of IDs that should be excluded from evaluation. The exclusion list is useful when a given member of the expression set triggers a false positive.
Preconfigured rule examples
The following expression uses the
xss-stable preconfigured rule
to mitigate XSS attacks:
The following expression uses all the expressions from the
preconfigured rule except for member IDs
evaluatePreconfiguredExpr('xss-stable', ['owasp-crs-v020901-id981136-xss', 'owasp-crs-v020901-id981138-xss'])
The following expression uses a preconfigured rule to mitigate SQLi attacks
198.51.100.0/24 IP address range:
inIpRange(origin.ip, '198.51.100.0/24') && evaluatePreconfiguredExpr('sqli-stable')
- For information on creating security policies and rules, see Configuring security policies and particularly the section Creating Google Cloud Armor security policies, rules, and expressions.
- For information on how to tune preconfigured WAF rules, see Tuning Google Cloud Armor WAF rules.