In-App WAF Rules


With Application Security Management (ASM) enabled, the Datadog tracing library actively monitors all web services and API requests for suspicious security activity.

An In-App WAF rule specifies conditions on the incoming request to define what the library considers suspicious. The Datadog tracing library includes hundreds of out-of-the-box ASM In-App WAF rules, which are used to display suspicious requests in the trace explorer and in the default signal rules.

You can add to the In-App WAF rules without upgrading the tracing library.

Structure of an ASM In-App WAF rule

An In-App WAF rule is a JSON object composed of a category, a name, tags, and conditions. When a suspicious request is detected, tags from the rules are propagated onto the suspicious request, and can be used to build detection rules.


Conditions define when the rule tags an incoming request. The conditions are composed of inputs and operators.


An input represents which part of the request the operator is applied to. The following inputs are used in the In-App WAF rules:

server.request.uri.rawThe full request URI received by the application service
server.request.path_paramsThe parsed path parameters (key/value map)userId => 1234
server.request.queryThe parsed query parameters (key/value map)clientId => 234
server.request.headers.no_cookiesThe incoming http requests headers, excluding the cookie header (key/value map)user-agent => Zgrab, referer =>
grpc.server.request.messageThe parsed gRPC message (key/value map)data.items[0] => value0, data.items[1] => value1
server.request.bodyThe parsed HTTP body (key/value map)data.items[0] => value0, data.items[1] => value1
server.response.statusThe http status code200


match_regexPerform regular expression match on the inputs
phrase_matchPerform a fast keyword list matching
is_xssSpecial operator to check for cross-site scripting (XSS) payloads
is_sqliSpecial operator to check for SQL injection (SQLI) payloads

Configure an ASM In-App WAF rule in your service

  1. In Datadog, navigate to the In-App WAF page under ASM Configuration.

  2. Click Download Configuration to download the configuration file, appsec-rules.json, to your local machine.

  3. Update the file to include the JSON definition of your new rule, following the specification above. For example:

            "id": "id-123",
            "name": "My In-App WAF rule",
            "tags": {
                "category": "attack_attempt",
                "crs_id": "920260",
                "type": "http_protocol_violation"
            "conditions": [
                    "operator": "match_regex",
                    "parameters": {
                        "inputs": [
                                "address": "server.request.uri.raw"
                        "options": {
                            "case_sensitive": true,
                            "min_length": 6
                        "regex": "\\%u[fF]{2}[0-9a-fA-F]{2}"
            "transformers": []
  4. Using a utility such as SCP or FTP, copy the appsec-rules.json file to your application server, for example, /home/asm/appsec-rules.json.

  5. Following the instructions in Enabling ASM for adding application variables in your environment, add the DD_APPSEC_RULES environment variable to your service with the full path to the file:

  6. Restart your service.

What to do next

Next, configure detection rules to create security signals based on those suspicious requests defined by the In-App WAF rules you created. You can modify the provided out-of-the-box ASM detection rules or create new ones.

Further Reading