CWE-221 Class Incomplete

Information Loss or Omission

This weakness occurs when an application fails to log critical security events or records them inaccurately, which can misguide security decisions and hinder incident investigation.

Definition

What is CWE-221?

This weakness occurs when an application fails to log critical security events or records them inaccurately, which can misguide security decisions and hinder incident investigation.
When a system doesn't capture key details like authentication failures, access violations, or input errors, security teams lose the visibility needed to detect and respond to attacks. This omission creates blind spots, making it difficult to understand an attack's origin, method, and impact, ultimately weakening your security posture. This problem can also be a side effect of another vulnerability. For instance, a severe issue like a buffer overflow might cause a program to crash abruptly before it has a chance to write any log entry about the anomalous event. This means the root cause remains hidden, complicating forensic analysis and delaying the fix for the underlying flaw.
Real-world impact

Real-world CVEs caused by CWE-221

  • CVE-2004-2227

    Web browser's filename selection dialog only shows the beginning portion of long filenames, which can trick users into launching executables with dangerous extensions.

  • CVE-2003-0412

    application server does not log complete URI of a long request (truncation).

  • CVE-1999-1029

    Login attempts are not recorded if the user disconnects before the maximum number of tries.

  • CVE-2002-0725

    Attacker performs malicious actions on a hard link to a file, obscuring the real target file.

  • CVE-1999-1055

    Product does not warn user when document contains certain dangerous functions or macros.

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 PHP

This code logs suspicious multiple login attempts.

Vulnerable PHP 
function login($userName,$password){
  		if(authenticate($userName,$password)){
  			return True;
  		}
  		else{
  			incrementLoginAttempts($userName);
  			if(recentLoginAttempts($userName) > 5){
  				writeLog("Failed login attempt by User: " . $userName . " at " + date('r') );
  			}
  		}
  }
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-221

  • 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-221

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-221 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-221?

This weakness occurs when an application fails to log critical security events or records them inaccurately, which can misguide security decisions and hinder incident investigation.

How serious is CWE-221?

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-221?

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

How can I prevent CWE-221?

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-221?

Plexicus's SAST engine matches the data-flow signature for CWE-221 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-221?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/221.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-221

CWE-664 Parent

Improper Control of a Resource Through its Lifetime

This vulnerability occurs when software fails to properly manage a resource throughout its entire lifecycle—from creation and active use…

CWE-118 Sibling

Incorrect Access of Indexable Resource ('Range Error')

This vulnerability occurs when software fails to properly check the boundaries of an indexed resource, like an array, buffer, or file,…

CWE-1229 Sibling

Creation of Emergent Resource

This vulnerability occurs when a system's normal operations unintentionally create new, exploitable resources that attackers can use to…

CWE-1250 Sibling

Improper Preservation of Consistency Between Independent Representations of Shared State

This vulnerability occurs when a system with multiple independent components (like distributed services or separate hardware units) each…

CWE-1329 Sibling

Reliance on Component That is Not Updateable

This vulnerability occurs when a product depends on a component that cannot be updated or patched to fix security flaws or critical bugs.

CWE-372 Sibling

Incomplete Internal State Distinction

This vulnerability occurs when an application fails to accurately track its own operational state. The system incorrectly assumes it's in…

CWE-400 Sibling

Uncontrolled Resource Consumption

This vulnerability occurs when an application fails to properly manage a finite resource, allowing an attacker to exhaust it and cause a…

CWE-404 Sibling

Improper Resource Shutdown or Release

This vulnerability occurs when a program fails to properly close or release a system resource—like a file handle, database connection, or…

CWE-410 Sibling

Insufficient Resource Pool

This vulnerability occurs when a system's resource pool is too small to handle maximum usage. Attackers can exploit this by making a high…

Resources

Further reading

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