CWE-356 Base Incomplete

Product UI does not Warn User of Unsafe Actions

This vulnerability occurs when a software interface fails to alert users before they perform a risky action. Without clear warnings, users can be more easily misled into taking steps that harm their…

Definition

What is CWE-356?

This vulnerability occurs when a software interface fails to alert users before they perform a risky action. Without clear warnings, users can be more easily misled into taking steps that harm their system or data.
A secure user interface acts as a safety checkpoint, clearly informing users when an action could be dangerous—like installing software from an untrusted source or permanently deleting critical data. These warnings should be prominent, use plain language, and require explicit user confirmation to proceed, helping prevent accidental or socially-engineered mistakes. For developers, this means building proactive confirmation dialogs or banners for high-risk operations such as file execution, financial transactions, or system changes. The warning should explain the specific risk (e.g., 'This file came from outside your organization') and offer a safe alternative, empowering users to make informed security decisions rather than blindly proceeding.
Real-world impact

Real-world CVEs caused by CWE-356

  • CVE-1999-1055

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

  • CVE-1999-0794

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

  • CVE-2000-0277

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

  • CVE-2000-0517

    Product does not warn user about a certificate if it has already been accepted for a different site. Possibly resultant.

  • CVE-2005-0602

    File extractor does not warn user if setuid/setgid files could be extracted. Overlaps privileges/permissions.

  • CVE-2000-0342

    E-mail client allows bypass of warning for dangerous attachments via a Windows .LNK file that refers to the attachment.

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-356

  • 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-356

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-356 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-356?

This vulnerability occurs when a software interface fails to alert users before they perform a risky action. Without clear warnings, users can be more easily misled into taking steps that harm their system or data.

How serious is CWE-356?

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-356?

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

How can I prevent CWE-356?

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-356?

Plexicus's SAST engine matches the data-flow signature for CWE-356 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-356?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/356.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-356

CWE-221 Parent

Information Loss or Omission

This weakness occurs when an application fails to log critical security events or records them inaccurately, which can misguide security…

CWE-222 Sibling

Truncation of Security-relevant Information

This vulnerability occurs when a system shortens or cuts off security-critical data during display, logging, or processing. This…

CWE-223 Sibling

Omission of Security-relevant Information

This vulnerability occurs when an application fails to capture or present crucial security-related details, such as the origin of a…

CWE-224 Sibling

Obscured Security-relevant Information by Alternate Name

This vulnerability occurs when a system logs or reports security-critical events using a nickname or alias for a component, instead of its…

CWE-396 Sibling

Declaration of Catch for Generic Exception

This weakness occurs when code catches a generic exception type like 'Exception' or 'Throwable', which can hide specific errors and create…

CWE-397 Sibling

Declaration of Throws for Generic Exception

This vulnerability occurs when a method is declared to throw an overly broad exception type, such as a generic 'Exception' or 'Throwable'.…

CWE-451 Sibling

User Interface (UI) Misrepresentation of Critical Information

This vulnerability occurs when a user interface fails to accurately display or highlight crucial information, potentially misleading users…

Resources

Further reading

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