AppSensor ResponseActions

About This Document

These response actions are part of the OWASP AppSensor project which advocates bringing intelligent intrusion detection inside the application. These responses can be used to counter a malicious user that has been detected probing for vulnerabilities or weaknesses within your application.

Overview

The following table lists possible AppSensor Responses (ASRs), other than no response (ASR-P). The application response actions are categorized here from the user's perspective (not from the application/server's perspective):

• Silent: User(s) unaware of any application change
• Passive: Process altered, but user(s) may still continue to process completion
• Active: Functionality reduced or disabled
• Intrusive: Non-malicious action on user's system

To add a response action, just use the next available letter (e.g. "ASR-Q") - they don't have to be in alphabetical order below, but place it in the appropriate category (silent, passive, active or intrusive). The image in the table below can be updated later to keep in step with the page content.

A text version of the table, with some examples and alternative classifications, is described in AppSensor - Response Actions (63 KB PDF). The information on the page below is likely to be more up-to-date.

Detailed Listing

Classifications are:

• Purposes: Logging, Notifying, Disrupting and Blocking
• Target: One, Some or All users
• Response duration: Instantaneous (e.g. just for the request), Period (e.g. time period or session duration), Permanent

Silent

ASR-P: No Response

id	ASR-P
title	No Response
classifications	(not applicable)
category	Silent
description	There is no response. This could be used to record in logs that a detection event did not lead to any particular response action.
consideration
examples	Example 1: A detection point fired, but the threshold for response has not been reached
code	-

ASR-A: Logging Change

id	ASR-A
title	Logging Change
classifications	Logging | One, some or all users | Instantaneous (request) or for a period
category	Silent
description	The granularity of logging is changed (typically more logging).
consideration
examples	Example 1: Capture sanitised request headers and response bodies Example 2: Full stack trace of error messages logged Example 3: Record DNS data on user's IP address Example 4: Security logging level changed to include 'informational' messages
code	-

ASR-B: Administrator Notification

id	ASR-B
title	Administrator Notification
classifications	Logging and notifying | One, some or all users | Instantaneous
category	Silent
description	A notification message is sent to the application administrator(s)
consideration
examples	Example 1: Email alert sent to everyone in the administration team Example 2: SMS alert sent to the on-call administrator Example 3: Visual indicator displayed on an application monitoring dashboard Example 4: Audible alarm in the control room
code	-

ASR-C: Other Notification

id	ASR-C
title	Other Notification
classifications	Logging and notifying | One user | Instantaneous
category	Silent
description	Notification message sent to something or someone other than Administrators (see ASR-B) or the User (see ASR-E)
consideration	The message recipient (e.g. firewall) could take some action otherwise unavailable to the application (e.g. disruptive - the application makes a silent response, but the firewall actively intervenes and perhaps blocks the user).
examples	Example 1: Broadcast event to SIEM Example 2: Signal sent to upstream network firewall, application firewall (e.g. XML, web) or load balancer Example 3: Alert sent to fraud protection department Example 4: Record added to server event log Example 5: Event highlighted in a daily management report Example 6: Email alert to staff member's manager Example 7: Proactive entry added to customer support system (e.g. "Someone had difficulty logging in with this customer's username - request extra validation for telephone enquiries")
code	-

ASR-N: Proxy

id	ASR-N
title	Proxy
classifications	Logging | One, some or all users | For a period or permanent
category	Silent
description	Send the request to a different back-end location. For redirection that the user will be aware of, see See ASR-G instead.
consideration
examples	Example 1: Requests from the user invisibly (from the user's perspective) passed through to a hardened system Example 2: Request are proxied to a special honeypot system which closely mimics or has identical user functionality
code	-

Passive

ASR-D: User Status Change

id	ASR-D
title	User Status Change
classifications	Logging | One user | For a period
category	Passive
description	A parameter related to the user is modified. This may have an impact on functionality or usability of the application, but only for the one user.
consideration
examples	Example 1: Internal trustworthiness scoring about the user changed Example 2: Reduce payment transfer limit for the customer before additional out-of-band verification is required Example 3: Reduce maximum file size limit for each file upload by the forum user Example 4: Increase data validation strictness for all form submissions by this citizen Example 5: Reduce the number of failed authentication attempts allowed before the user's account is locked (ASR-K below)
code	-

ASR-E: User Notification

id	ASR-E
title	User Notification
classifications	Logging, notifying and disrupting | One user | Instantaneous
category	Passive
description	A visual, audible and/or mechanical (e.g. vibration) signal or message is activated, displayed, or sent by other means, to the user.
consideration
examples	Example 1: On-screen message about mandatory form fields (e.g. "The 'occupation' must be completed") Example 2: On-screen message about data validation issues (e.g. 'The bank sort code can only contain six digits with optional hyphens') Example 3: Message sent by email to the registered email address to inform them their password has been changed Example 4: On-screen message warning that they have been detected performing malicious activity (e.g. Mr Clippy idea)
code	-

ASR-F: Timing Change

id	ASR-F
title	Timing Change
classifications	Logging and disrupting | One, some or all users | Instantaneous (request) or for a period
category	Passive
description	The usual timescales to perform an operation are altered, usually extended, or delays are added.
consideration
examples	Example 1: Extend response time for each failed authentication attempt Example 2: File upload process duration extended artificially Example 3: Add fixed time delay into every response Example 4: Order flagged for manual checking Example 5: Goods despatch put on hold (e.g. despatch status changed)
code	-

Active

ASR-G: Process Terminated

id	ASR-G
title	Process Terminated
classifications	Logging, notifying (sometimes) and disrupting | One user | Instantaneous
category	Active
description	An interruption to the sending, display or process, such that the user has to start again, or start somewhere else. For authenticated users, this would not include termination of their session (see ASR-J). And, they would be free to attempt the process again (e.g. access the resource after logging in, submit a payment transfer, etc).
consideration
examples	Example 1: Discard data, display message and force user to begin business process from start Example 2: Redirection of an unauthenticated user to the log-in page Example 3: Redirection to home page Example 4: Display other content (i.e. terminate process but display the output of some other page without redirect) Example 5: Redirection to a page on another website
code	-

ASR-H: Function Amended

id	ASR-H
title	Function Amended
classifications	Logging, notifying (sometimes), disrupting and blocking | One, some or all users | For a period or permanent
category	Active
description	The usual functionality is amended but not disabled (see ASR-I).
consideration
examples	Example 1: Limit on feature usage rate imposed Example 2: Reduce number of times/day the user can submit a review Example 3: Additional registration identity validation steps Example 4: Additional anti-automation measures (e.g. out-of-band verification activated, CAPTCHA introduced) Example 5: Static rather than dynamic content returned Example 6: Additional validation requirements for delivery address Example 7: Watermarks added to pages, images and other content Example 8: Additional human interactive proof challenges added due to the number of incorrect guesses of CAPTCHAs outnumbering the correct guesses by more than a certain factor (e.g. Token bucket idea) Example 9: Fuzz responses to mask real functionality or increase attacker efforts to enumerate the application (e.g. random URL generation using ADHD Spider Trap or Weblabyrinth, realistic but invalid cipher text data using techniques such as honey encryption)
code	-

ASR-I: Function Disabled

id	ASR-I
title	Function Disabled
classifications	Logging, notifying (sometimes), disrupting and blocking | One, some or all users | For a period or permanent
category	Active
description	A function or functions are disabled for one, some or all users. Other functionality continues to work as normal.
consideration	For changes that affect multiple users, be careful the response cannot be used too easily for denial of service.
examples	Example 1: 'Add friend' feature inactivated Example 2: 'Recommend to a colleague' feature links removed and disabled Example 3: Document library search disabled Example 4: Prevent new site registrations Example 5: Web service inactivated or cloaked Example 6: Content syndication stopped Example 7: Automated Direct Debit system turned off and manual form offered instead
code	-

ASR-J: Account Logout

id	ASR-J
title	Account Logout
classifications	Logging, notifying (sometimes), disrupting and blocking | One user | Instantaneous
category	Active
description	The current session is terminated on the server, and the user is logged out.
consideration	Often undertaken in conjunction with process termination (ASR-G) and sometimes lockout (ASR-K).
examples	Example 1: Session terminated and user redirected to logged-out message page Example 2: Session terminated only (no redirect)
code	-

ASR-K: Account Lockout

id	ASR-K
title	Account Lockout
classifications	Logging, notifying (sometimes), disrupting and blocking | One user | For a period or permanent
category	Active
description	An account, session or source address is blocked from access and/or authentication.
consideration	If IP blocking is implemented, it is recommended this is undertaken at the network layer using the operating system (e.g. iptables, Windows firewall) or by a network device (e.g. firewall).
examples	Example 1: User account locked for 10 minutes Example 2: User account locked permanently until an Administrator resets it Example 3: One user's IP address range blocked Example 4: Unauthenticated user's session terminated
code	-

ASR-L: Application Disabled

id	ASR-L
title	Application Disabled
classifications	Logging, notifying (sometimes), disrupting and blocking | All users | Permanent
category	Active
description	The whole application is disabled or made unavailable.
consideration	Be careful the response cannot be used too easily for denial of service.
examples	Example 1: Website shut down and replaced with temporary static page Example 2: Application taken offline
code	-

Intrusive

ASR-M: Collect Data from User

id	ASR-M
title	Collect Data from User
classifications	Logging | One user | For a period
category	Intrusive
description	Direct action to collect further information from the user's system.
consideration	This response is meant to be non-malicious in intent - it is simply additional information gathering - and not retaliatory or damaging to the user, their systems or data, nor make any permanent change. An alert user might be aware of the action. Be very wary of data collected and perform appropriate validation and sanitization. Ensure any use of this type of response is legally permissible in the relevant jurisdictions, and complies with corporate policies and the application's terms of use, privacy notice and corporate policies. To a certain extent, any additional payload in a response might cause a user's browser or computer to crash, and this might have unforeseen circumstances. The information collection could use techniques like these described elsewhere: Panopticlick methods to gather information on the user's browser and computer configuration Response content injection using JavaScript to discover the user's real IP address Embeddable decloaking engine to discover the real IP address of a web user Using ModSecurity and BeEF to monitor an attacker
examples	Example 1: Deploy additional browser fingerprinting using JavaScript in responses Example 2: Deploy a Java applet to collect remote IP address Example 3: Deploy JavaScript to collect information about the user's network Example 4: Record mobile phone fingerprint and IMEI number
code	-