Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
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
-
Web browser's filename selection dialog only shows the beginning portion of long filenames, which can trick users into launching executables with dangerous extensions.
-
application server does not log complete URI of a long request (truncation).
-
Login attempts are not recorded if the user disconnects before the maximum number of tries.
-
Attacker performs malicious actions on a hard link to a file, obscuring the real target file.
-
Product does not warn user when document contains certain dangerous functions or macros.
How attackers exploit it
Step-by-step attacker path
- 1
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 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.
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
// 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
Run dynamic application security testing against the live endpoint.
Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.
Code review: flag any new code that handles input from this surface without using the validated framework helpers.
CWE-221
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Frequently asked questions What is CWE-221?
How serious is CWE-221?
What languages or platforms are affected by CWE-221?
How can I prevent CWE-221?
How does Plexicus detect and fix CWE-221?
Where can I learn more about CWE-221?
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…
Ready to validate what matters?
Ready to validate what matters?
Plexicus is Proof-Driven AppSec: validated findings, contextual understanding, and reviewed remediation — anchored in evidence, scoped with you.