What is Reliance on a Single Factor (CWE-654)?

TL;DR: Reliance on a Single Factor in a Security Decision (CWE-654) is a vulnerability where security mechanisms rely solely on one factor, making them vulnerable if that factor is compromised.

What is Reliance on a Single Factor in a Security Decision?

Reliance on a Single Factor in a Security Decision (CWE-654) is a type of vulnerability where security mechanisms rely exclusively, or to a large extent, on the evaluation of a single condition or the integrity of a single object or entity. As defined by the MITRE Corporation under CWE-654, and classified by the OWASP Foundation under [no mapping], this weakness undermines the integrity of security decisions.

Quick Summary

Reliance on a Single Factor in a Security Decision compromises security mechanisms if a single factor is compromised. It can lead to unauthorized access and non-repudiation issues. Jump to: Overview · How it Works · Business Impact · Attack Scenario · Detection · Fixes

Jump to: Quick Summary · Reliance on a Single Factor in a Security Decision Overview · How Reliance on a Single Factor in a Security Decision Works · Business Impact of Reliance on a Single Factor in a Security Decision · Reliance on a Single Factor in a Security Decision Attack Scenario · How to Detect Reliance on a Single Factor in a Security Decision · How to Fix Reliance on a Single Factor in a Security Decision · Framework-Specific Fixes for Reliance on a Single Factor in a Security Decision · How to Ask AI to Check Your Code for Reliance on a Single Factor in a Security Decision · Reliance on a Single Factor in a Security Decision Best Practices Checklist · Reliance on a Single Factor in a Security Decision FAQ · Vulnerabilities Related to Reliance on a Single Factor in a Security Decision · References · Scan Your Own Site

Reliance on a Single Factor in a Security Decision Overview

What

Reliance on a Single Factor in a Security Decision occurs when security mechanisms depend solely on one factor to make decisions, such as possession of a token or verification of a single condition.

Why it matters

A compromised single factor can lead to unauthorized access and non-repudiation issues, making it difficult to distinguish between legitimate and illegitimate activities.

Where it occurs

This weakness is common in applications that rely on single-factor authentication mechanisms without additional checks.

Who is affected

Developers and security professionals who implement or review such systems are at risk if they overlook the need for multiple factors.

Who is NOT affected

Applications that use multi-factor authentication (MFA) and redundant access rules are not vulnerable to this weakness.

How Reliance on a Single Factor in a Security Decision Works

Root Cause

Security mechanisms rely solely on one factor, making them susceptible to compromise if the single factor is breached or spoofed.

Attack Flow

1. Attacker identifies the single-factor security mechanism.
2. Attacker compromises or spoofs the single factor.
3. Attacker gains unauthorized access by bypassing the compromised security mechanism.

Prerequisites to Exploit

• The application must rely solely on one factor for security decisions.
• The attacker must have a way to compromise or spoof that single factor.

Vulnerable Code

def grant_access(token):
    if token == 'valid_token':
        return True

This code grants access based solely on the presence of a valid token, without additional checks.

Secure Code

def grant_access(token, second_factor):
    if token == 'valid_token' and verify_second_factor(second_factor):
        return True

The secure version requires both a valid token and an additional factor to be verified before granting access.

Business Impact of Reliance on a Single Factor in a Security Decision

Confidentiality

• Exposed sensitive data: Unauthorized access can lead to disclosure of confidential information.
• Compromised user credentials: Stolen tokens or compromised factors expose users’ personal data.

Integrity

• Unauthorized modifications: Attackers can modify system configurations or data without proper authorization.
• Data tampering: Illegitimate activities are indistinguishable from legitimate ones, leading to potential data corruption.

Availability

• Service disruptions: Compromised single-factor mechanisms can be used to disrupt services by unauthorized users.
• System downtime: Unauthorized access can lead to denial of service attacks.

Reliance on a Single Factor in a Security Decision Attack Scenario

1. Attacker identifies the application relies solely on token-based authentication.
2. Attacker steals or spoofs the valid token.
3. Attacker uses the compromised token to gain unauthorized access to the system.
4. The attacker performs illegitimate activities, such as modifying sensitive data.

How to Detect Reliance on a Single Factor in a Security Decision

Manual Testing

• Review security mechanisms for single-factor checks.
• Verify that multiple factors are used before granting access or privileges.

Automated Scanners (SAST/DAST)

Static analysis can identify configurations relying solely on one protection method. Dynamic testing confirms if the mechanism is actually exploitable at runtime.

PenScan Detection

PenScan’s scanners such as ZAP, Nuclei, and Wapiti detect reliance on single-factor mechanisms in web applications.

False Positive Guidance

A finding is real if the security mechanism relies solely on one factor without additional checks. A false positive occurs when a multi-factor system appears to rely on a single factor due to configuration issues.

How to Fix Reliance on a Single Factor in a Security Decision

• Use multiple simultaneous checks before granting access or privileges.
• Implement redundant access rules on different choke points (e.g., firewalls).
• Enforce least privilege and role-based access control for critical operations.

Framework-Specific Fixes for Reliance on a Single Factor in a Security Decision

public boolean grantAccess(String token, String secondFactor) {
    if (token.equals("valid_token") && verifySecondFactor(secondFactor)) {
        return true;
    }
    return false;
}

def grant_access(token, second_factor):
    if token == 'valid_token' and verify_second_factor(second_factor):
        return True
    return False

How to Ask AI to Check Your Code for Reliance on a Single Factor in a Security Decision

Reliance on a Single Factor in a Security Decision Best Practices Checklist

✅ Use multiple factors to verify user identity before granting access. ✅ Implement redundant access rules at different levels of the system. ✅ Enforce least privilege principles for critical operations. ✅ Verify second-factor integrity and authenticity. ✅ Regularly review security mechanisms for single-factor reliance.

Reliance on a Single Factor in a Security Decision FAQ

How does reliance on a single factor affect security decisions?

It undermines the integrity of security mechanisms by making them vulnerable to compromise if that single factor is breached or spoofed.

Can you provide an example of reliance on a single factor in real-world applications?

An application that grants access based solely on possession of a physical token without additional verification can be exploited if the token is stolen.

What are the common consequences of relying on a single factor for security decisions?

It leads to unauthorized access and non-repudiation issues, making it difficult to distinguish legitimate from illegitimate activities.

How do you detect reliance on a single factor in an application?

Manual testing involves reviewing security mechanisms for single-factor checks, while automated scanners can identify configurations that rely solely on one protection method.

What are the best practices for preventing reliance on a single factor?

use multiple simultaneous or successive checks to enhance security.

How does reliance on a single factor impact confidentiality and integrity in an application?

It exposes sensitive data and allows unauthorized modifications, compromising both confidentiality and integrity of the system.

What are some common vulnerabilities related to reliance on a single factor?

CWE-657 Violation of Secure Design Principles and CWE-693 Protection Mechanism Failure often coexist with this issue.

Vulnerabilities Related to Reliance on a Single Factor in a Security Decision

| CWE | Name | Relationship | |—|—|—| | 657 | Violation of Secure Design Principles | ChildOf | | 693 | Protection Mechanism Failure | ChildOf |

References

• MITRE - CWE-654
• NVD - NIST

Scan Your Own Site

Manual code review catches what you know to look for. An automated scan catches what you didn’t. Scan your own website using PenScan to find Reliance on a Single Factor in a Security Decision and other risks before an attacker does.