Reliance on Untrusted Inputs in a Security Decision| ID: 807 | Date: (C)2012-05-14 (M)2022-10-10 |
| Type: weakness | Status: INCOMPLETE |
| Abstraction Type: Base |
Description
The application uses a protection mechanism that relies on the
existence or values of an input, but the input can be modified by an untrusted
actor in a way that bypasses the protection mechanism.
Extended DescriptionDevelopers may assume that inputs such as cookies, environment variables,
and hidden form fields cannot be modified. However, an attacker could change
these inputs using customized clients or other attacks. This change might
not be detected. When security decisions such as authentication and
authorization are made based on the values of these inputs, attackers can
bypass the security of the software.Without sufficient encryption, integrity checking, or other mechanism, any
input that originates from an outsider cannot be trusted.
Likelihood of Exploit: Medium to High
Applicable PlatformsLanguage Class: Language-independent
Time Of Introduction
- Architecture and Design
- Implementation
Related Attack Patterns
Common Consequences
| Scope | Technical Impact | Notes |
|---|
| ConfidentialityAccess_ControlAvailabilityOther | Bypass protection
mechanismGain privileges / assume
identityVaries by context | Attackers can bypass the security decision to access whatever is being
protected. The consequences will depend on the associated functionality,
but they can range from granting additional privileges to untrusted
users to bypassing important security checks. Ultimately, this weakness
may lead to exposure or modification of sensitive data, system crash, or
execution of arbitrary code. |
Detection Methods
| Name | Description | Effectiveness | Notes |
|---|
| Manual Static Analysis | Since this weakness does not typically appear frequently within a
single software package, manual white box techniques may be able to
provide sufficient code coverage and reduction of false positives if all
potentially-vulnerable operations can be assessed within limited time
constraints. | High | |
Potential Mitigations
| Phase | Strategy | Description | Effectiveness | Notes |
|---|
| Architecture and Design | Identify and Reduce Attack Surface | Store state information and sensitive data on the server side only.Ensure that the system definitively and unambiguously keeps track of
its own state and user state and has rules defined for legitimate state
transitions. Do not allow any application user to affect state directly
in any way other than through legitimate actions leading to state
transitions.If information must be stored on the client, do not do so without
encryption and integrity checking, or otherwise having a mechanism on
the server side to catch tampering. Use a message authentication code
(MAC) algorithm, such as Hash Message Authentication Code (HMAC)
[R.807.2]. Apply this against the state or sensitive data that you have
to expose, which can guarantee the integrity of the data - i.e., that
the data has not been modified. Ensure that you use an algorithm with a
strong hash function (CWE-328). | | |
| Architecture and Design | 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.With a stateless protocol such as HTTP, use a framework that maintains
the state for you.Examples include ASP.NET View State [R.807.3] and the OWASP ESAPI
Session Management feature [R.807.4].Be careful of language features that provide state support, since
these might be provided as a convenience to the programmer and may not
be considering security. | | |
| Architecture and Design | | For any security checks that are performed on the client side, ensure
that these checks are duplicated on the server side, in order to avoid
CWE-602. Attackers can bypass the client-side checks by modifying values
after the checks have been performed, or by changing the client to
remove the client-side checks entirely. Then, these modified values
would be submitted to the server. | | |
| OperationImplementation | Environment Hardening | When using PHP, configure the application so that it does not use
register_globals. During implementation, develop the application so that
it does not rely on this feature, but be wary of implementing a
register_globals emulation that is subject to weaknesses such as CWE-95,
CWE-621, and similar issues. | | |
| Architecture and DesignImplementation | Identify and Reduce Attack Surface | Understand all the potential areas where untrusted inputs can enter
your software: parameters or arguments, cookies, anything read from the
network, environment variables, reverse DNS lookups, query results,
request headers, URL components, e-mail, files, filenames, databases,
and any external systems that provide data to the application. Remember
that such inputs may be obtained indirectly through API calls.Identify all inputs that are used for security decisions and determine
if you can modify the design so that you do not have to rely on
submitted inputs at all. For example, you may be able to keep critical
information about the user's session on the server side instead of
recording it within external data. | | |
Relationships
| Related CWE | Type | View | Chain |
|---|
| CWE-807 ChildOf CWE-859 | Category | CWE-844 | |
Demonstrative Examples (Details)
- In the following example, an authentication flag is read from a
browser cookie, thus allowing for external control of user state
data. (Demonstrative Example Id DX-17)
- The following code could be for a medical records application. It
performs authentication by checking if a cookie has been set. (Demonstrative Example Id DX-16)
- The following code excerpt reads a value from a browser cookie to
determine the role of the user. (Demonstrative Example Id DX-15)
- The following code samples use a DNS lookup in order to decide
whether or not an inbound request is from a trusted host. If an attacker can
poison the DNS cache, they can gain trusted status. (Demonstrative Example Id DX-93)
Observed Examples
- CVE-2009-1549 : Attacker can bypass authentication by setting a cookie to a specific value.
- CVE-2009-1619 : Attacker can bypass authentication and gain admin privileges by setting an "admin" cookie to 1.
- CVE-2009-0864 : Content management system allows admin privileges by setting a "login" cookie to "OK."
- CVE-2008-5784 : e-dating application allows admin privileges by setting the admin cookie to 1.
- CVE-2008-6291 : Web-based email list manager allows attackers to gain admin privileges by setting a login cookie to "admin."
For more examples, refer to CVE relations in the bottom box.
White Box Definitions None
Black Box Definitions None
Taxynomy Mappings
| Taxynomy | Id | Name | Fit |
|---|
| CERT C++ Secure Coding | ENV03-CPP | Sanitize the environment when invoking external
programs | |
| CERT Java Secure Coding | SEC09-J | Do not base security checks on untrusted
sources | |
References:
- Frank Kim .Top 25 Series - Rank 6 - Reliance on Untrusted Inputs in a
Security Decision. SANS Software Security Institute. 2010-03-05.
- .HMAC. Wikipedia. 2011-08-18.
- Scott Mitchell .Understanding ASP.NET View State. Microsoft. 2004-05-15.
- OWASP .OWASP Enterprise Security API (ESAPI) Project.
