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CRV2 ActiveDefense

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Active Defense

Attack detection undertaken at the application layer has access to the complete context of an interaction and enhanced information about the user. The application knows what is a high-value issue and what is noise. Input data are already decrypted and canonicalized within the application and therefore application-specific intrusion detection is less susceptible to advanced evasion techniques. This leads to a very low level of attack identification false positives, providing appropriate detection points are selected.

The fundamental requirements are the ability to perform four tasks:

  • Detection of a selection of suspicious and malicious events
  • Use of this knowledge centrally to identify attacks
  • Selection of a predefined response
  • Execution of the response.

Applications can undertake a range of responses, that may include changes to a user's account or other changes to the application's defensive posture. It can be difficult to detect active defense in dynamic analysis since the responses may be invisible to the tester. Code review is the best method to determine the existence of this defense.

Other application functionality like authentication failure counts and lock-out, or limits on rate of file uploads are localized protection mechanisms. This sort of standalone logic is not active defense equivalents in the context of this review, unless they are rigged together into an application-wide sensory network and centralized analytical engine.

It is not a bolt-on tool or code library, but instead offers insight to an approach for organizations to specify or develop their own implementations – specific to their own business, applications, environments and risk profile – building upon existing standard security controls. However, some developers may have used the following components:

Purpose of Code Review

In this case, a code review is being used to detect the presence of a defense, and it is the absence of this that is a weakness. Note that active defense cannot defend an application that has known vulnerabilities, and therefore the other parts of this guide are extremely important. The code reviewer should note the absence of active defense as a vulnerability.

The purpose of code review is not necessarily to determine the efficacy of the active defense, but could simply be to determine if such capability exists.

How to Locate the Attack Detection and Response Code

Detection Points

Detection points can be integrated into presentation, business and data layers of the application. Application-specific intrusion detection does not need to identify all invalid usage, to be able to determine an attack. There is no need for “infinite data” or “big data” and therefore the location of "detection points" may be very sparse within source code.

A useful approach for identifying such code is to find the name of the only guidance in this area by searching for the string:


Additionally search for AppSensor's detection point type identities:

  RE1, RE2, ... RE8
  AE1, AE2, ... AE12
  SE1, SE2, ... SE6
  ACE1, ACE2, ... ACE4
  IE1, IE2, ... IE6
  EE1, EE2
  CIE1, CIE2, ... CIE4
  FIO1, FIO2
  HT1, HT2, HT3
  UT1, UT2, ... UT4
  STE1, STE2, STE3
  RP1, RP2, RP3, RP4

Additionally search for any tagging based on Mitre's Common Attack Pattern Enumeration and Classification (CAPEC) such as strings like:

  CAPEC-212, CAPEC-213, etc

The AppSensor detection point type identifiers and CAPEC codes will often have been used in configuration values (e.g. in ESAPI for Java), parameter names and security event classification. Also, examine error logging and security event logging mechanisms as these may be being used to collect data that can then be used for attack detection. Identify the code or services called that perform this logging and examine the event properties recorded/sent. Then identify all places where these are called from.

An examination of error handling code relating to input and output validation is very likely to reveal the presence of detection points. For example, in a whitelist type of detection point, additional code may have been added adjacent, or within error handling code flow:

 if ( var !Match this ) {
     Error handling
     Record event for attack detection

In some situations attack detection points are looking for blacklisted input, and the test may not exist otherwise, so brand new code is added:

 if ( var !Match that ) {
     Record event for attack detection

Identification of detection points should also have found the locations where events are recorded (the "event store").

If detection points cannot be found, continue to review the code for execution of response, as this may provide insight into the existence of active defense.

Attack Identification

The event store has to be analysed in real time or very frequently, in order to identify attacks based on predefined criteria. The criteria should be defined in configuration settings (e.g. in configuration files, or read from another source such as a database).

A process will examine the event store to determine if an attack is in progress - typically this will be attempting to identify an authenticated user, but it may also consider a single IP address, range of IP addresses, or groups of users such as one or more roles, users with a particular privilege or even all users.

Selection of Response

Once an attack has been identified, the response will be selected based on predefined criteria. Again an examination of configuration data should reveal the thresholds related to each detection point, groups of detection points or overall thresholds.

Additionally search for AppSensor's response type identities as they may have been used in configuration settings, parameter names or in logical operations:

  ASR-A, ASR-B, ... ASR-N, ASR-P

The most common response actions are user warning messages, log out, account lockout and administrator notification. However, as this approach is connected into the application, the possibilities of response actions are limited only by the coded capabilities of the application.

Execution of Response

Search code for any global includes that poll attack identification/response identified above. Response actions (agains a user, IP address, group of users, etc) will usually be initiated by the application, but in some cases other applications (e.g. alter a fraud setting) or infrastructure components (e.g. block an IP address range) may also be involved.

Examine configuration files and any external communication the application performs. The following types of responses may have been coded:

  • Logging increased
  • Administrator notification
  • Other notification (e.g. other system)
  • Proxy
  • User status change
  • User notification
  • Timing change
  • Process terminated (same as traditional defenses)
  • Function amended
  • Function disabled
  • Account log out
  • Account lock out
  • Application disabled
  • Collect data from user.

Other capabilities of the application and related system components can be repurposed or extended, to provide the selected response actions. Therefore review the code associated with any localised security measures such as account lock out.

Leading Practice for Active Defense

The guidance for adding active response to applications given in the OWASP_AppSensor_Project, and in particular the AppSensor Guide v2.