External Control of Critical State Data

Opis

The product stores security-critical state information about its users, or the product itself, in a location that is accessible to unauthorized actors.

If an attacker can modify the state information without detection, then it could be used to perform unauthorized actions or access unexpected resources, since the application programmer does not expect that the state can be changed.

State information can be stored in various locations such as a cookie, in a hidden web form field, input parameter or argument, an environment variable, a database record, within a settings file, etc. All of these locations have the potential to be modified by an attacker. When this state information is used to control security or determine resource usage, then it may create a vulnerability. For example, an application may perform authentication, then save the state in an "authenticated=true" cookie. An attacker may simply create this cookie in order to bypass the authentication.

Skutki

• Access Control

  Bypass Protection Mechanism; Gain Privileges or Assume Identity

  An attacker could potentially modify the state in malicious ways. If the state is related to the privileges or level of authentication that the user has, then state modification might allow the user to bypass authentication or elevate privileges.

• Confidentiality

  Read Application Data

  The state variables may contain sensitive information that should not be known by the client.

• Availability

  DoS: Crash, Exit, or Restart

  By modifying state variables, the attacker could violate the application's expectations for the contents of the state, leading to a denial of service due to an unexpected error condition.

Zapobieganie

• Architecture and Design

  Understand all the potential locations that are accessible to attackers. For example, some programmers assume that cookies and hidden form fields cannot be modified by an attacker, or they may not consider that environment variables can be modified before a privileged program is invoked.

• 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

  Store state information 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.

• 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 [REF-1482].

  With a stateless protocol such as HTTP, use some frameworks can maintain the state for you.

  Examples include ASP.NET View State and the OWASP ESAPI Session Management feature.

  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.

Przykłady podatności

• CVE-2005-2428 Mail client stores password hashes for unrelated accounts in a hidden form field.
• CVE-2008-0306 Privileged program trusts user-specified environment variable to modify critical configuration settings.
• CVE-1999-0073 Telnet daemon allows remote clients to specify critical environment variables for the server, leading to code execution.
• CVE-2007-4432 Untrusted search path vulnerability through modified LD_LIBRARY_PATH environment variable.
• CVE-2006-7191 Untrusted search path vulnerability through modified LD_LIBRARY_PATH environment variable.
• CVE-2008-5738 Calendar application allows bypass of authentication by setting a certain cookie value to 1.
• CVE-2008-5642 Setting of a language preference in a cookie enables path traversal attack.
• CVE-2008-5125 Application allows admin privileges by setting a cookie value to "admin."
• CVE-2008-5065 Application allows admin privileges by setting a cookie value to "admin."
• CVE-2008-4752 Application allows admin privileges by setting a cookie value to "admin."
• CVE-2000-0102 Shopping cart allows price modification via hidden form field.
• CVE-2000-0253 Shopping cart allows price modification via hidden form field.
• CVE-2008-1319 Server allows client to specify the search path, which can be modified to point to a program that the client has uploaded.

Słabość nadrzędna

• CWE-668 Exposure of Resource to Wrong Sphere

Słabości podrzędne

• CWE-15 External Control of System or Configuration Setting
• CWE-73 External Control of File Name or Path
• CWE-426 Untrusted Search Path
• CWE-472 External Control of Assumed-Immutable Web Parameter
• CWE-565 Reliance on Cookies without Validation and Integrity Checking

Kiedy powstaje

• Architecture and Design — OMISSION: This weakness is caused by missing a security tactic during the architecture and design phase.
• Implementation

Dotyczy

Not Language-Specific, Web Server

Źródła

1. Top 10 2007-Insecure Direct Object Reference — OWASP, 2007
2. HMAC — Wikipedia, 2011
3. 24 Deadly Sins of Software Security — Michael Howard, David LeBlanc, John Viega, "Sin 4: Use of Magic URLs, Predictable Cookies, and Hidden Form Fields." Page 75, McGraw-Hill, 2010
4. D3FEND: D3-TL Trusted Library — D3FEND