The software performs an authorizationcheck when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions.
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 incorrectly applied, 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 correctly 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 correctly restricted, or by
accessing insufficiently-protected, privileged functionality to write
the data.
Access Control
Technical Impact: Gain privileges / assume
identity; Bypass protection
mechanism
An attacker could gain privileges by modifying or reading critical
data directly, or by accessing 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. Even if they can be customized to
recognize these schemes, they might not be able to tell whether the
scheme correctly performs the authorization in a way that cannot be
bypassed or subverted by an attacker.
Effectiveness: Limited
Automated Dynamic Analysis
Automated dynamic analysis may not be able to find interfaces that are
protected by authorization checks, even if those checks contain
weaknesses.
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
The following code could be for a medical records application. It
displays a record to already authenticated users, confirming the user's
authorization using a value stored in a cookie.
(Bad Code)
Example
Language: PHP
$role = $_COOKIES['role'];
if (!$role) {
$role = getRole('user');
if ($role) {
// save the cookie to send out in future responses
setcookie("role", $role, time()+60*60*2);
}
else{
ShowLoginScreen();
die("\n");
}
}
if ($role == 'Reader') {
DisplayMedicalHistory($_POST['patient_ID']);
}
else{
die("You are not Authorized to view this record\n");
}
The programmer expects that the cookie will only be set when
getRole() succeeds. The programmer even diligently specifies a 2-hour
expiration for the cookie. However, the attacker can easily set the
"role" cookie to the value "Reader". As a result, the $role variable is
"Reader", and getRole() is never invoked. The attacker has bypassed the
authorization system.
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) [R.863.1] 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 access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied 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 [R.863.2].
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.863.4] and the OWASP ESAPI Access Control feature [R.863.5].
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.863.6] [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.
Description
