What is Authentication Bypass by Alternate Name (CWE-289)?

TL;DR: Authentication Bypass by Alternate Name (CWE-289) occurs when a system fails to validate all possible alternate names for resources or actors, allowing attackers to bypass authentication mechanisms.

What is Authentication Bypass by Alternate Name?

Authentication Bypass by Alternate Name (CWE-289) is a type of vulnerability where the product performs authentication based on the name of a resource being accessed or the name of the actor performing the access, but it does not properly check all possible names for that resource or actor. As defined by the MITRE Corporation under CWE-289, and classified by the OWASP Foundation under A07:2025 - Authentication Failures…

Quick Summary

Authentication Bypass by Alternate Name is a critical vulnerability where an attacker can bypass authentication mechanisms by exploiting alternate names for resources or actors. This allows unauthorized access to sensitive data and actions. Jump to: Overview · How It Works · Business Impact · Attack Scenario · Detection · Fixes

Jump to: Quick Summary · Authentication Bypass by Alternate Name Overview · How Authentication Bypass by Alternate Name Works · Business Impact of Authentication Bypass by Alternate Name · Authentication Bypass by Alternate Name Attack Scenario · How to Detect Authentication Bypass by Alternate Name · How to Fix Authentication Bypass by Alternate Name · Framework-Specific Fixes for Authentication Bypass by Alternate Name · How to Ask AI to Check Your Code for Authentication Bypass by Alternate Name · Authentication Bypass by Alternate Name Best Practices Checklist · Authentication Bypass by Alternate Name FAQ · Vulnerabilities Related to Authentication Bypass by Alternate Name · References · Scan Your Own Site

Authentication Bypass by Alternate Name Overview

• What: A system performs authentication based on resource or actor names but fails to validate all possible alternate names.
• Why it matters: This vulnerability allows attackers to bypass protection mechanisms and gain unauthorized access.
• Where it occurs: In web applications, file systems, and any environment where resource or actor names are used for authentication.
• Who is affected: Any application that relies on resource or actor names without proper validation.
• Who is NOT affected: Systems already using strict input validation and canonicalization strategies.

How Authentication Bypass by Alternate Name Works

Root Cause

The root cause of this vulnerability lies in the failure to validate all possible alternate names for resources or actors before performing sensitive operations. This can include hard links, symbolic links, NTFS/HFS alternate data streams, etc.

Attack Flow

1. An attacker identifies a resource or actor name that has an alternate representation.
2. The attacker uses this alternate name in the authentication process to bypass validation checks.
3. Unauthorized access is granted due to the failure to validate all possible names.

Prerequisites to Exploit

• The system must use resource or actor names for authentication.
• There must be a way to create or discover alternate representations of these names (e.g., hard links, symbolic links).

Vulnerable Code

path = request.form['file_path']
os.chmod(path, 0o755)

This code is vulnerable because it does not validate the file_path input against all possible alternate names before performing a sensitive operation like changing file permissions.

Secure Code

import os.path

def get_canonical_name(file_path):
    return os.path.realpath(os.path.abspath(file_path))

path = request.form['file_path']
canonical_path = get_canonical_name(path)
os.chmod(canonical_path, 0o755)

This secure code ensures that the file_path input is transformed into its canonical form before performing any sensitive operations.

Business Impact of Authentication Bypass by Alternate Name

• Confidentiality: Unauthorized access to sensitive data.
• Integrity: Modification of critical resources or actions performed under different identities.
• • Financial losses due to unauthorized transactions.
  • Compliance violations and legal penalties for security breaches.
  • Damage to reputation and loss of customer trust.

Authentication Bypass by Alternate Name Attack Scenario

1. An attacker identifies a resource with an alternate name (e.g., symbolic link).
2. The attacker uses this alternate name in the authentication process to bypass validation checks.
3. Unauthorized access is granted, allowing the attacker to modify or delete sensitive files.

How to Detect Authentication Bypass by Alternate Name

Manual Testing

• • Verify that all possible resource names are validated before granting access.
  • Check if the system properly handles alternate representations of resource names (e.g., hard links).

Automated Scanners (SAST / DAST)

Static analysis can detect hardcoded or predictable resource names, while dynamic testing can identify runtime vulnerabilities.

PenScan Detection

PenScan’s scanners such as ZAP and Wapiti actively check for paths that allow unauthorized access through alternate names.

False Positive Guidance

A false positive occurs when a system properly validates all possible alternate names but still flags the pattern due to incomplete detection logic.

How to Fix Authentication Bypass by Alternate Name

• Avoid making decisions based on resource or actor names if those resources can have alternate names.
• Assume all input is malicious and use an “accept known good” validation strategy.
• Inputs should be decoded, canonicalized, and validated strictly before being used in sensitive operations.

Framework-Specific Fixes for Authentication Bypass by Alternate Name

Python/Django

def get_canonical_name(file_path):
    return os.path.realpath(os.path.abspath(file_path))

path = request.form['file_path']
canonical_path = get_canonical_name(path)
os.chmod(canonical_path, 0o755)

How to Ask AI to Check Your Code for Authentication Bypass by Alternate Name

Authentication Bypass by Alternate Name Best Practices Checklist

• ✅ Avoid making decisions based on resource or actor names if those resources can have alternate names.
• ✅ Assume all input is malicious and use an “accept known good” validation strategy.
• ✅ Inputs should be decoded, canonicalized, and validated strictly before being used in sensitive operations.

Authentication Bypass by Alternate Name FAQ

How does Authentication Bypass by Alternate Name occur?

It occurs when a system performs authentication based on the name of a resource or actor but fails to account for all possible alternate names.

What are some real-world examples of Authentication Bypass by Alternate Name?

Examples include using hard links, symbolic links, or NTFS/HFS alternate data streams to bypass file access controls.

How can I detect Authentication Bypass by Alternate Name in my application?

Use manual testing techniques and automated scanners like ZAP and Wapiti to identify paths that allow unauthorized access through alternate names.

What is the primary fix for Authentication Bypass by Alternate Name?

Ensure all possible alternate names are validated before performing any sensitive operations on resources or actors.

How can I prevent Authentication Bypass by Alternate Name in my codebase?

Implement input validation strategies to reject inputs that do not conform to strict specifications and canonicalize inputs properly.

What manual testing steps should I follow to find Authentication Bypass by Alternate Name vulnerabilities?

Check if your application validates all possible resource names before granting access or performing sensitive operations.

How can I use AI to check my code for Authentication Bypass by Alternate Name?

Review the following Python code block for potential CWE-289 vulnerabilities and rewrite it using input validation techniques:

Vulnerabilities Related to Authentication Bypass by Alternate Name

References

• https://cwe.mitre.org/data/definitions/289.html
• https://owasp.org/Top10/2025/A07_2025-Authentication_Failures/
• https://nvd.nist.gov/

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 Authentication Bypass by Alternate Name and other risks before an attacker does.