CWE-305 Base Draft

Authentication Bypass by Primary Weakness

This vulnerability occurs when a system's core authentication logic is technically correct, but an attacker can completely bypass it by exploiting a separate, more fundamental flaw in the application.

Definition

What is CWE-305?

This vulnerability occurs when a system's core authentication logic is technically correct, but an attacker can completely bypass it by exploiting a separate, more fundamental flaw in the application.
Think of this as a strong lock on a weak door. The authentication mechanism itself isn't broken, but a critical oversight elsewhere—like an unprotected alternative login path, a logic flaw in session handling, or misconfigured security controls—provides a direct route around it. Attackers target these primary weaknesses first, rendering the robust authentication process irrelevant because they never have to pass through it. For developers, this means security auditing must look beyond just the login function. You must examine the entire authentication flow, including password reset endpoints, API tokens, session validation, and any hidden administrative interfaces. The fix involves identifying and securing that primary entry point, ensuring all access paths enforce the same rigorous checks as your main login system.
Real-world impact

Real-world CVEs caused by CWE-305

  • CVE-2002-1374

    The provided password is only compared against the first character of the real password.

  • CVE-2000-0979

    The password is not properly checked, which allows remote attackers to bypass access controls by sending a 1-byte password that matches the first character of the real password.

  • CVE-2001-0088

    Chain: Forum software does not properly initialize an array, which inadvertently sets the password to a single character, allowing remote attackers to easily guess the password and gain administrative privileges.

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable pseudo

MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.

Vulnerable pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
Secure code example

Secure pseudo

Secure pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-305

  • Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
  • Implementation Validate input at trust boundaries; use allowlists, not denylists.
  • Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
  • Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
  • Operation Monitor logs for the runtime signals listed in the next section.
Detection signals

How to detect CWE-305

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-305 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-305?

This vulnerability occurs when a system's core authentication logic is technically correct, but an attacker can completely bypass it by exploiting a separate, more fundamental flaw in the application.

How serious is CWE-305?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-305?

MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.

How can I prevent CWE-305?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

How does Plexicus detect and fix CWE-305?

Plexicus's SAST engine matches the data-flow signature for CWE-305 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-305?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/305.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-305

CWE-1390 Parent

Weak Authentication

This vulnerability occurs when a system's login or identity verification process is too easy to bypass or fool. While it attempts to check…

CWE-1391 Sibling

Use of Weak Credentials

This vulnerability occurs when a system relies on weak authentication credentials—like default passwords, hard-coded keys, or easily…

CWE-262 Sibling

Not Using Password Aging

This vulnerability occurs when a system lacks password expiration policies, allowing users to keep the same password indefinitely.

CWE-263 Sibling

Password Aging with Long Expiration

The system enforces password changes, but the time allowed between changes is excessively long, weakening security.

CWE-289 Sibling

Authentication Bypass by Alternate Name

This vulnerability occurs when a system checks access based on a resource or user name, but fails to account for all the different names…

CWE-290 Sibling

Authentication Bypass by Spoofing

This weakness occurs when an application's authentication system can be tricked into accepting forged or manipulated credentials, allowing…

CWE-294 Sibling

Authentication Bypass by Capture-replay

This vulnerability occurs when an attacker can intercept and record legitimate authentication traffic, then replay it later to gain…

CWE-301 Sibling

Reflection Attack in an Authentication Protocol

A reflection attack is a flaw in mutual authentication protocols that allows an attacker to impersonate a legitimate user without knowing…

CWE-302 Sibling

Authentication Bypass by Assumed-Immutable Data

This vulnerability occurs when an authentication system incorrectly treats certain data as unchangeable, when in fact an attacker can…

Resources

Further reading

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