CWE-1390 Class Incomplete

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 who a user claims to be, the checks are insufficient,…

Definition

What is CWE-1390?

This vulnerability occurs when a system's login or identity verification process is too easy to bypass or fool. While it attempts to check who a user claims to be, the checks are insufficient, allowing attackers to impersonate legitimate users.
Weak authentication creates a critical security gap by failing to reliably verify user identity. Attackers can exploit this flaw using methods like brute-forcing simple passwords, reusing stolen credentials, or bypassing login pages entirely, often with minimal time or resources. This undermines the entire security model, as access controls are built on the faulty assumption that the user's identity is proven. For developers, this means your authentication mechanism must actively resist common attacks. Implement strong, multi-factor authentication (MFA), enforce robust password policies, and use secure, time-limited sessions. Regularly audit and test your login flows to ensure they cannot be circumvented with automated tools or known exploitation techniques.
Real-world impact

Real-world CVEs caused by CWE-1390

  • CVE-2022-30034

    Chain: Web UI for a Python RPC framework does not use regex anchors to validate user login emails (CWE-777), potentially allowing bypass of OAuth (CWE-1390).

  • CVE-2022-35248

    Chat application skips validation when Central Authentication Service (CAS) is enabled, effectively removing the second factor from two-factor authentication

  • CVE-2021-3116

    Chain: Python-based HTTP Proxy server uses the wrong boolean operators (CWE-480) causing an incorrect comparison (CWE-697) that identifies an authN failure if all three conditions are met instead of only one, allowing bypass of the proxy authentication (CWE-1390)

  • CVE-2022-29965

    Distributed Control System (DCS) uses a deterministic algorithm to generate utility passwords

  • CVE-2022-29959

    Initialization file contains credentials that can be decoded using a "simple string transformation"

  • CVE-2020-8994

    UART interface for AI speaker uses empty password for root shell

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-1390

  • 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-1390

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-1390 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-1390?

This vulnerability occurs when a system's login or identity verification process is too easy to bypass or fool. While it attempts to check who a user claims to be, the checks are insufficient, allowing attackers to impersonate legitimate users.

How serious is CWE-1390?

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-1390?

MITRE lists the following affected platforms: ICS/OT, Not Technology-Specific.

How can I prevent CWE-1390?

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-1390?

Plexicus's SAST engine matches the data-flow signature for CWE-1390 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-1390?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1390.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-1390

CWE-287 Parent

Improper Authentication

Improper Authentication occurs when a system fails to properly verify a user's claimed identity, allowing access without sufficient proof…

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-295 Sibling

Improper Certificate Validation

This vulnerability occurs when an application fails to properly verify the authenticity of a digital certificate, or performs the…

CWE-306 Sibling

Missing Authentication for Critical Function

This vulnerability occurs when a software feature that performs a sensitive action or uses significant system resources does not verify…

CWE-307 Sibling

Improper Restriction of Excessive Authentication Attempts

This vulnerability occurs when an application fails to properly limit how many times someone can attempt to log in or verify their…

CWE-521 Sibling

Weak Password Requirements

This vulnerability occurs when an application fails to enforce strong password policies, making user accounts easier to compromise through…

CWE-522 Sibling

Insufficiently Protected Credentials

This vulnerability occurs when an application handles sensitive credentials like passwords or API keys in an insecure way, making them…

CWE-640 Sibling

Weak Password Recovery Mechanism for Forgotten Password

This vulnerability occurs when an application's password reset or recovery feature is poorly designed or implemented, allowing attackers…

Resources

Further reading

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