Improper Enforcement of Behavioral Workflow

The software supports a session in which more than one behavior must be performed by an actor, but it does not properly ensure that the actor performs the behaviors in the required sequence.


Description

By performing actions in an unexpected order, or by omitting steps, an attacker could manipulate the business logic of the software or cause it to enter an invalid state. In some cases, this can also expose resultant weaknesses.

For example, a file-sharing protocol might require that an actor perform separate steps to provide a username, then a password, before being able to transfer files. If the file-sharing server accepts a password command followed by a transfer command, without any username being provided, the software might still perform the transfer.

Note that this is different than CWE-696, which focuses on when the software performs actions in the wrong sequence; this entry is closely related, but it is focused on ensuring that the actor performs actions in the correct sequence.

Workflow-related behaviors include:

Steps are performed in the expected order.

Required steps are not omitted.

Steps are not interrupted.

Steps are performed in a timely fashion.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

This code is part of an FTP server and deals with various commands that could be sent by a user. It is intended that a user must successfully login before performing any other action such as retrieving or listing files.

def dispatchCommand(command, user, args):

  if command == 'Login':
    loginUser(args)
    return


  # user has requested a file
  if command == 'Retrieve_file':
    if authenticated(user) and ownsFile(user,args):
    sendFile(args)
    return

  if command == 'List_files':
    listFiles(args)
    return

  ...

The server correctly does not send files to a user that isn't logged in and doesnt own the file. However, the server will incorrectly list the files in any directory without confirming the command came from an authenticated user, and that the user is authorized to see the directory's contents.

Here is a fixed version of the above example:

def dispatchCommand(command, user, args):


  ...
  if command == 'List_files':
    if authenticated(user) and ownsDirectory(user,args):
      listFiles(args)
      return


  ...

See Also

User Session Errors

Weaknesses in this category are related to session management. Frequently these deal with the information or status about each user and their access rights for the dur...

Manage User Sessions

Weaknesses in this category are related to the design and architecture of session management. Frequently these deal with the information or status about each user and ...

Business Logic Errors

Weaknesses in this category identify some of the underlying problems that commonly allow attackers to manipulate the business logic of an application. Errors in busine...

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

CWE Cross-section

This view contains a selection of weaknesses that represent the variety of weaknesses that are captured in CWE, at a level of abstraction that is likely to be useful t...


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