Reliance on Untrusted Inputs in a Security Decision

Opis

The product 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.

Developers 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.

Skutki

• Confidentiality, Access Control, Availability, Other

  Bypass Protection Mechanism; Gain Privileges or Assume Identity; Varies 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.

Zapobieganie

• Architecture and Design · Attack Surface Reduction

  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) [REF-529]. Apply this against the state or sensitive data that has to be exposed, which can guarantee the integrity of the data - i.e., that the data has not been modified. Ensure that a strong hash function is used (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 [REF-756] and the OWASP ESAPI Session Management feature [REF-45].

  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.

• Operation, Implementation · 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 Design, Implementation · Attack Surface Reduction

  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.

Przykłady podatności

• 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."

Słabość nadrzędna

• CWE-693 Protection Mechanism Failure

Słabości podrzędne

• CWE-302 Authentication Bypass by Assumed-Immutable Data
• CWE-350 Reliance on Reverse DNS Resolution for a Security-Critical Action
• CWE-784 Reliance on Cookies without Validation and Integrity Checking in a Security Decision

Kiedy powstaje

• Architecture and Design — COMMISSION: This weakness refers to an incorrect design related to an architectural security tactic.
• Implementation

Dotyczy

Not Language-Specific, Not Technology-Specific, Web Based, Web Server

Źródła

1. Top 25 Series - Rank 6 - Reliance on Untrusted Inputs in a Security Decision — Frank Kim, SANS Software Security Institute, 2010
2. HMAC — Wikipedia, 2011
3. Understanding ASP.NET View State — Scott Mitchell, Microsoft, 2004
4. OWASP Enterprise Security API (ESAPI) Project — OWASP
5. State-of-the-Art Resources (SOAR) for Software Vulnerability Detection, Test, and Evaluation — Gregory Larsen, E. Kenneth Hong Fong, David A. Wheeler, Rama S. Moorthy, 2014