Configuring Web Application security is easily done via the configuration wizard, and in the vast majority of the cases, is enough to fully protect the web assets without additional manual changes.
However, as event logs appear, a security administrator might want to make specific exceptions to the default behavior of the system, regardless of the automatic learning mechanism.
Configuring Exceptions Upon Log
The most common use case of exception configuration is when a log is issued and as a security administrator decided that traffic matching one of the log fields (for example, the URI field) should not be detected or blocked by the open-appsec engine.
Step 1: From the events view, perform a "Right Click" on the relevant parameter in the log according to which the exclusion should occur and select "Add Exception"
Step 2: Review the exception details and click OK
A common change might be to generalize the exception to all sources by deleting the condition for "Source Identifier", or to change the action from "Skip" (relevant only for the "Matched Parameter" field) to "Accept".
An exception configured this way applies to the combination of the specific open-appsec security practice that caught the original event and the Asset relevant for the same traffic.
For further information on how to configure exceptions from asset view and the full options an exception can provide, please read further.
Possible actions for exception rules
Accept - Traffic matching the exception's conditions will be accepted.
Drop - Traffic matching the exception's conditions will be blocked.
Skip - Relevant only for specific keys like "Parameter Name", "Parameter Value" and "Indicator. Allows skipping the value of the matching parameter from being inspected by the AppSec engines.
The rest of the traffic will be inspected for malicious behavior.
Suppress Log - Traffic matching the exception's condition will not activate their Log Trigger object/s upon event.
Possible conditions for exception rules
Keys
There are several keys allowed to be set in exceptions rules, each of them may be relevant to a different security practice or sub-practice.
IPS Exceptions Scope
Exceptions for requests that are blocked or detected by IPS are evaluated only against the following attributes:
protectionName – The name of the signature
hostName – The HTTP host name (if available)
sourceIP – The client IP address (if available)
url – The HTTP decoded path (if available)
sourceIdentifier – The source identifier (if available)
Any additional attributes defined in an exception (for example, HTTP method) are not supported for IPS and are ignored.
As a result, a request may still be blocked by IPS even if an exception is defined using unsupported fields.
IP address of the request's source in IP address or CIDR format (e.g. "<IP address>/<number of bits for network>")
No
All open-appsec Security
Parameter Name
Regular Expression of a parameter name is a key in the HTTP request body's XML or JSON file
Yes
Web and API attacks, and Schema Validation
Parameter Value
Regular Expression of a parameter value is the value to a key in the HTTP request body's XML or JSON file
Yes
Web and API attacks, and Schema Validation
Parameter Location
A value that matches the "Matched Location" field values in a the open-appsec Log (e.g. "body", "cookie", "url", etc.)
Yes
Web and API attacks
Indicator
Regular expression of indicator/s to be be used with the "Skip" action. Allows exclusion of desired indicators while continuing to provide security for all other traffic.
Yes
Web and API attacks
Protection Name
The protection name used by the security sub-practice
No
IPS and Snort Rules only
Country Code
Country is resolved according to the source IP address. Code is the recommended use for country-based exceptions and can be searched here according to the Alpha-2 code of ISO-3166.
No
All open-appsec Security (not including IPS)
Country Name
Country is resolved according to the source IP address. Name is less recommended for country-based exceptions, but is more readable. Exact names can be searched here according to ISO-3166.
No
All open-appsec Security (not including IPS)
File Hash
SHA-256 string of the file the exception should apply to.
No
File Security only
File Name
The file name to match the configured exception.
No
File Security only
Response Body
Note - Scanning response traffic adds a performance impact.
Regular expression of a pattern within the HTTP Response Body
All All open-appsec Security (not including IPS)-appsec Security
Regular Expression Values
The following is only relevant for keys where the table states their value is a regular expression.
When an exception key expects a regular expression value (regex), it should be configured according to PCRE 2.0, which will undergo a partial search unless the '^' or '$' regular expression operators are used.
For a nicer tutorial about PCRE regular expression crafting, visit here.
Operators
A complex logical expression with "AND" and "OR" between conditions can be created.
In addition - the following operators are available for each condition:
Equals
Not Equals
Key Exists
View And Configure Exceptions In Assets
Configuring exceptions
Step 1: Browse to Assets, edit an existing asset and click on the "Custom Rules and Exceptions" tab
Step 2: Click to add a new exception
Step 3: Create the exclusion according to the options described in this page
When clicking the 3 dotted lines you will see the logical operators available for multiple conditions:
When clicking on the ':' between key and value you will see the additional value-based operators for a single condition:
Add a comment for view purposes and click OK.
Viewing Exceptions
When exceptions are configured, the same location in the asset provides a view of the exceptions for the practice used by the asset. The view shows the comment and the last administrator that edited the exception:
Save Exception for Reuse In Additional Assets/Practices
It is possible to save a group of exception rules under a global name, and then use the same object by multiple assets and practices.
Configure an Existing Exception as Global
Step 1: Click on the 3 dots in the top right corner of the exceptions view
Step 2: Click Save and give a name to the new global "Exceptions" object
Step 3: In additional assets you can now click "Load" in the same location and select an existing "Custom Rules and Exceptions" object
View and Manage Global Exceptions Objects
The global exceptions objects can be viewed and edited under Behaviors:
