CWE-302 Base Incomplete

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 manipulate it to bypass login or verification checks.

Definition

What is CWE-302?

This vulnerability occurs when an authentication system incorrectly treats certain data as unchangeable, when in fact an attacker can manipulate it to bypass login or verification checks.
Developers often assume that specific data points, like hidden form fields, environment variables, or certain HTTP headers, are secure and cannot be altered by a user. However, attackers can intercept and modify this 'assumed-immutable' data during transit or exploit client-side controls, tricking the application into granting unauthorized access. To prevent this, never trust client-side data for critical security decisions. Always re-validate authentication state and user permissions on the server using a trusted, server-controlled session mechanism. Treat all data from the client—including cookies, headers, and hidden parameters—as potentially malicious and subject to verification against the authoritative server-side session store.
Real-world impact

Real-world CVEs caused by CWE-302

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 Java

In the following example, an "authenticated" cookie is used to determine whether or not a user should be granted access to a system.

Vulnerable Java 
boolean authenticated = new Boolean(getCookieValue("authenticated")).booleanValue();
  if (authenticated) {
  	...
  }
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-302

  • Architecture and Design / Operation / Implementation Implement proper protection for immutable data (e.g. environment variable, hidden form fields, etc.)
Detection signals

How to detect CWE-302

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-302 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-302?

This vulnerability occurs when an authentication system incorrectly treats certain data as unchangeable, when in fact an attacker can manipulate it to bypass login or verification checks.

How serious is CWE-302?

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-302?

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

How can I prevent CWE-302?

Implement proper protection for immutable data (e.g. environment variable, hidden form fields, etc.)

How does Plexicus detect and fix CWE-302?

Plexicus's SAST engine matches the data-flow signature for CWE-302 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-302?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/302.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-302

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-303 Sibling

Incorrect Implementation of Authentication Algorithm

This weakness occurs when a developer implements a standard authentication algorithm, but makes critical mistakes in the code that cause…

Resources

Further reading

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