CWE-645 Base Incomplete High likelihood

Overly Restrictive Account Lockout Mechanism

This vulnerability occurs when an application's account lockout feature is too strict, allowing attackers to easily trigger it and lock legitimate users out of their accounts, causing a denial of…

Definition

What is CWE-645?

This vulnerability occurs when an application's account lockout feature is too strict, allowing attackers to easily trigger it and lock legitimate users out of their accounts, causing a denial of service.
Account lockout is a common defense against password-guessing attacks, temporarily disabling an account after several failed login attempts. However, if configured too aggressively—with a very low attempt threshold or an excessively long lockout period—this protective measure can be turned against the system itself. Attackers can exploit this by intentionally failing login attempts for targeted user accounts, denying access to legitimate users. To prevent this, developers must balance security with usability, ensuring lockout policies are strict enough to deter brute-force attacks but not so restrictive that they enable easy denial-of-service.
Real-world impact

Real-world CVEs caused by CWE-645

No public CVE references are linked to this CWE in MITRE's catalog yet.

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-645

  • Architecture and Design Implement more intelligent password throttling mechanisms such as those which take IP address into account, in addition to the login name.
  • Architecture and Design Implement a lockout timeout that grows as the number of incorrect login attempts goes up, eventually resulting in a complete lockout.
  • Architecture and Design Consider alternatives to account lockout that would still be effective against password brute force attacks, such as presenting the user machine with a puzzle to solve (makes it do some computation).
Detection signals

How to detect CWE-645

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-645 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-645?

This vulnerability occurs when an application's account lockout feature is too strict, allowing attackers to easily trigger it and lock legitimate users out of their accounts, causing a denial of service.

How serious is CWE-645?

MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.

What languages or platforms are affected by CWE-645?

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

How can I prevent CWE-645?

Implement more intelligent password throttling mechanisms such as those which take IP address into account, in addition to the login name. Implement a lockout timeout that grows as the number of incorrect login attempts goes up, eventually resulting in a complete lockout.

How does Plexicus detect and fix CWE-645?

Plexicus's SAST engine matches the data-flow signature for CWE-645 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-645?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/645.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-645

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-1390 Sibling

Weak Authentication

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CWE-290 Sibling

Authentication Bypass by Spoofing

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CWE-294 Sibling

Authentication Bypass by Capture-replay

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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…

Resources

Further reading

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