Reliance on a Single Factor in a Security Decision
Weakness ID: 654 (Weakness Base)Status: Draft
+ Description

Description Summary

A protection 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.

+ Time of Introduction
  • Architecture and Design
  • Implementation
  • Operation
+ Applicable Platforms



+ Common Consequences

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.


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.

+ 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).

+ 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).

+ 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.

+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfCategoryCategory254Security Features
Development Concepts699
ChildOfWeakness ClassWeakness Class657Violation of Secure Design Principles
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfWeakness ClassWeakness Class693Protection Mechanism Failure
Research Concepts1000
ParentOfWeakness BaseWeakness Base308Use of Single-factor Authentication
Research Concepts1000
ParentOfWeakness BaseWeakness Base309Use of Password System for Primary Authentication
Research Concepts1000
+ Causal Nature


+ References
Jerome H. Saltzer and Michael D. Schroeder. "The Protection of Information in Computer Systems". Proceedings of the IEEE 63. September, 1975. <>.
Sean Barnum and Michael Gegick. "Separation of Privilege". 2005-12-06. <>.
+ Content History
Submission DateSubmitterOrganizationSource
2008-01-18Pascal MeunierPurdue UniversityExternal Submission
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time of Introduction
2008-09-08CWE Content TeamMITREInternal
updated Alternate Terms, Common Consequences, Relationships, Other Notes, Weakness Ordinalities
2009-01-12CWE Content TeamMITREInternal
updated Description, Name
2009-05-27CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2009-01-12Design Principle Violation: Reliance on a Single Factor in a Security Decision