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 servicehttps://my.api.com/users/1234/roles?clientId=234
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 => google.com
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

Custom in-app WAF rules

Note: This feature is in beta.

Custom in-app WAF rules enable users to log specific types of requests to their applications. For example, you can use custom rules to monitor login success or failure. To get started, navigate to Security –> Application Security –> Configuration –> In-App WAF -> Custom Rules.

Note: Default rules in in-app WAF are read-only. Sometimes, to fine-tune your in-app WAF behavior, you need to modify the in-app WAF rules. While you cannot modify the default rules, you can create a custom rule based on one of the default rules and modify the match conditions as per your needs. Be sure to disable the default rule so that you don’t end up with two very similar rules evaluating the same requests.

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