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Design Principle Violation: Reliance on a Single Factor in a Security Decision Status: Draft Weakness ID: 654 (Weakness Base)Description Summary A security mechanism relies exclusively, or to a large extent, on the evaluation of a single condition or the integrity of a single object or entity in order to make a decision about granting access to restricted resources or functionality. Alternate Terms Separation of Privilege Some people and publications use the term "Separation of Privilege" to describe this weakness, but this term has dual meanings in current usage. While this node is closely associated with the original definition of "Separation of Privilege" by Saltzer and Schroeder, others use the same term to describe poor compartmentalization (CWE-653). Because there are multiple interpretations, use of the "Separation of Privilege" term is discouraged. Weakness Ordinalities Primary (where the weakness exists independent of other weaknesses) Causal Nature Implicit Common Consequences Integrity If the single factor is compromised (e.g. by theft or spoofing), then the integrity of the entire security mechanism can be violated with respect to the user that is identified by that factor. Accountability It can become difficult or impossible for the product to be able to distinguish between legitimate activities by the entity who provided the factor, versus illegitimate activities by an attacker. Potential Mitigations Use multiple simultaneous checks before granting access to critical operations or granting critical privileges. A weaker but helpful mitigation is to use several successive checks (multiple layers of security). Use redundant access rules on different choke points (e.g., firewalls). Demonstrative Examples Example 1: Password-only authentication is perhaps the most well-known example of use of a single factor. Anybody who knows a user's password can impersonate that user. Example 2: When authenticating, use multiple factors, such as "something you know" (such as a password) and "something you have" (such as a hardware-based one-time password generator, or a biometric device). Other Notes This node is closely associated with the term "Separation of Privilege." This term is used in several different ways in the industry, but they generally combine two closely related principles: compartmentalization (CWE-653) and using only one factor in a security decision (this node). Proper compartmentalization implicitly introduces multiple factors into a security decision, but there can be cases in which multiple factors are required for authentication or other mechanisms that do not involve compartmentalization, such as performing all required checks on a submitted certificate. It is likely that CWE-653 and CWE-654 will provoke further discussion. References Jerome H. Saltzer and
Michael D. Schroeder. "The Protection of Information in Computer Systems". Proceedings of the IEEE 63. September, 1975. <http:/ Sean Barnum and
Michael Gegick. "Separation of Privilege". 2005-12-06. <https:/ Relationships
Applicable Platforms Languages All Time of Introduction  Architecture and Design Implementation OperationContent History Submissions Pascal Meunier. Purdue University. 2008-01-18. (External Submission) Modifications Eric Dalci. Cigital. 2008-07-01. (External) updated Time_of_Introduction CWE Content Team. MITRE. 2008-09-08. (Internal) updated Alternate_Terms, Common_Consequences, Relationships, Other_Notes, Weakness_Ordinalities |
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