CWE-921 Base Incomplete

Storage of Sensitive Data in a Mechanism without Access Control

This vulnerability occurs when an application saves sensitive information to a storage location that lacks proper access restrictions, allowing unauthorized users or applications to view or modify…

Definition

What is CWE-921?

This vulnerability occurs when an application saves sensitive information to a storage location that lacks proper access restrictions, allowing unauthorized users or applications to view or modify the data.
Many modern storage systems use access controls to protect data, but not all do. Physical or removable media like USB drives, memory cards, and optical discs often provide full access to any user on the system. In multi-user environments, storing sensitive data on these uncontrolled mechanisms means anyone with system access can potentially read, copy, or alter that information. On Android, a common example is using external storage (like shared device storage or SD cards). This storage is typically globally readable and writable by all apps on the device. Furthermore, the data can often be accessed directly if the device is connected via USB to a computer or if the physical memory card is removed and read by another device.
Real-world impact

Real-world CVEs caused by CWE-921

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-921

  • 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-921

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-921 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-921?

This vulnerability occurs when an application saves sensitive information to a storage location that lacks proper access restrictions, allowing unauthorized users or applications to view or modify the data.

How serious is CWE-921?

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-921?

MITRE lists the following affected platforms: Mobile.

How can I prevent CWE-921?

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-921?

Plexicus's SAST engine matches the data-flow signature for CWE-921 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-921?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/921.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-921

CWE-922 Parent

Insecure Storage of Sensitive Information

This vulnerability occurs when an application stores sensitive data—like credentials, personal information, or encryption keys—without…

CWE-312 Sibling

Cleartext Storage of Sensitive Information

This vulnerability occurs when an application stores sensitive data like passwords, credit card numbers, or personal information in plain…

Resources

Further reading

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