The software does not perform or incorrectly performs an authorizationcheck when an actor attempts to access a resource or perform an action.
Extended Description
Assuming a user with a given identity, authorization is the process of determining whether that user can access a given resource, based on the user's privileges and any permissions or other access-control specifications that apply to the resource.
When access control checks are not applied consistently - or not at all - users are able to access data or perform actions that they should not be allowed to perform. This can lead to a wide range of problems, including information exposures, denial of service, and arbitrary code execution.
Alternate Terms
AuthZ:
"AuthZ" is typically used as an abbreviation of "authorization" within
the web application security community. It is also distinct from
"AuthC," which is an abbreviation of "authentication." The use of "Auth"
as an abbreviation is discouraged, since it could be used for either
authentication or authorization.
Time of Introduction
Architecture and Design
Implementation
Operation
Applicable Platforms
Languages
Language-independent
Technology Classes
Web-Server: (Often)
Database-Server: (Often)
Modes of Introduction
A developer may introduce authorization weaknesses because of a lack of
understanding about the underlying technologies. For example, a developer
may assume that attackers cannot modify certain inputs such as headers or
cookies.
Authorization weaknesses may arise when a single-user application is
ported to a multi-user environment.
Common Consequences
Scope
Effect
Confidentiality
Technical Impact: Read application
data; Read files or
directories
An attacker could read sensitive data, either by reading the data
directly from a data store that is not properly restricted, or by
accessing insufficiently-protected, privileged functionality to read the
data.
Integrity
Technical Impact: Modify application
data; Modify files or
directories
An attacker could modify sensitive data, either by writing the data
directly to a data store that is not properly restricted, or by
accessing insufficiently-protected, privileged functionality to write
the data.
Access Control
Technical Impact: Gain privileges / assume
identity
An attacker could gain privileges by modifying or reading critical
data directly, or by accessing insufficiently-protected, privileged
functionality.
Likelihood of Exploit
High
Detection Methods
Automated Static Analysis
Automated static analysis is useful for detecting commonly-used idioms
for authorization. A tool may be able to analyze related configuration
files, such as .htaccess in Apache web servers, or detect the usage of
commonly-used authorization libraries.
Generally, automated static analysis tools have difficulty detecting
custom authorization schemes. In addition, the software's design may
include some functionality that is accessible to any user and does not
require an authorization check; an automated technique that detects the
absence of authorization may report false positives.
Effectiveness: Limited
Automated Dynamic Analysis
Automated dynamic analysis may find many or all possible interfaces
that do not require authorization, but manual analysis is required to
determine if the lack of authorization violates business logic
Manual Analysis
This weakness can be detected using tools and techniques that require
manual (human) analysis, such as penetration testing, threat modeling,
and interactive tools that allow the tester to record and modify an
active session.
Specifically, manual static analysis is useful for evaluating the
correctness of custom authorization mechanisms.
Effectiveness: Moderate
These may be more effective than strictly automated techniques. This
is especially the case with weaknesses that are related to design and
business rules. However, manual efforts might not achieve desired code
coverage within limited time constraints.
Demonstrative Examples
Example 1
This function runs an arbitrary SQL query on a given database,
returning the result of the query.
(Bad Code)
Example
Language: PHP
function runEmployeeQuery($dbName, $name){
mysql_select_db($dbName,$globalDbHandle) or die("Could not
open Database".$dbName);
//Use a prepared statement to avoid CWE-89
$preparedStatement = $globalDbHandle->prepare('SELECT
* FROM employees WHERE name = :name');
While this code is careful to avoid SQL Injection, the function does
not confirm the user sending the query is authorized to do so. An
attacker may be able to obtain sensitive employee information from the
database.
Example 2
The following program could be part of a bulletin board system that
allows users to send private messages to each other. This program intends to
authenticate the user before deciding whether a private message should be
displayed. Assume that LookupMessageObject() ensures that the $id argument
is numeric, constructs a filename based on that id, and reads the message
details from that file. Also assume that the program stores all private
messages for all users in the same directory.
# For purposes of this example, assume that CWE-309
and
# CWE-523 do not apply.
if (! AuthenticateUser($q->param('username'),
$q->param('password'))) {
ExitError("invalid username or password");
}
my $id = $q->param('id');
DisplayPrivateMessage($id);
While the program properly exits if authentication fails, it does not
ensure that the message is addressed to the user. As a result, an
authenticated attacker could provide any arbitrary identifier and read
private messages that were intended for other users.
One way to avoid this problem would be to ensure that the "to" field
in the message object matches the username of the authenticated user.
Chain: SNMP product does not properly parse a
configuration option for which hosts are allowed to connect, allowing
unauthorized IP addresses to connect.
Chain: product does not properly check the result of a reverse DNS lookup because of operator precedence (CWE-783), allowing bypass of DNS-based access restrictions.
Potential Mitigations
Phase: Architecture and Design
Divide the software into anonymous, normal, privileged, and
administrative areas. Reduce the attack surface by carefully mapping
roles with data and functionality. Use role-based access control (RBAC)
to enforce the roles at the appropriate boundaries.
Note that this approach may not protect against horizontal
authorization, i.e., it will not protect a user from attacking others
with the same role.
Phase: Architecture and Design
Ensure that you perform access control checks related to your business
logic. These checks may be different than the access control checks that
you apply to more generic resources such as files, connections,
processes, memory, and database records. For example, a database may
restrict access for medical records to a specific database user, but
each record might only be intended to be accessible to the patient and
the patient's doctor.
Phase: Architecture and Design
Strategy: Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to
occur or provides constructs that make this weakness easier to
avoid.
For example, consider using authorization frameworks such as the JAAS Authorization Framework [R.285.5] and the OWASP ESAPI Access Control feature [R.285.4].
Phase: Architecture and Design
For web applications, make sure that the access control mechanism is
enforced correctly at the server side on every page. Users should not be
able to access any unauthorized functionality or information by simply
requesting direct access to that page.
One way to do this is to ensure that all pages containing sensitive
information are not cached, and that all such pages restrict access to
requests that are accompanied by an active and authenticated session
token associated with a user who has the required permissions to access
that page.
Phases: System Configuration; Installation
Use the access control capabilities of your operating system and
server environment and define your access control lists accordingly. Use
a "default deny" policy when defining these ACLs.
Background Details
An access control list (ACL) represents who/what has permissions to a
given object. Different operating systems implement (ACLs) in different
ways. In UNIX, there are three types of permissions: read, write, and
execute. Users are divided into three classes for file access: owner, group
owner, and all other users where each class has a separate set of rights. In
Windows NT, there are four basic types of permissions for files: "No
access", "Read access", "Change access", and "Full control". Windows NT
extends the concept of three types of users in UNIX to include a list of
users and groups along with their associated permissions. A user can create
an object (file) and assign specified permissions to that object.
[R.285.6] [REF-7] Mark Dowd, John McDonald
and Justin Schuh. "The Art of Software Security Assessment". Chapter 2, "Common Vulnerabilities of Authorization", Page
39.. 1st Edition. Addison Wesley. 2006.
[R.285.7] [REF-7] Mark Dowd, John McDonald
and Justin Schuh. "The Art of Software Security Assessment". Chapter 11, "ACL Inheritance", Page 649.. 1st Edition. Addison Wesley. 2006.
Description
