CWE-591 Variant Draft

Sensitive Data Storage in Improperly Locked Memory

This vulnerability occurs when an application stores sensitive information, like passwords or encryption keys, in system memory that isn't properly secured from being written to disk. If the memory…

Definition

What is CWE-591?

This vulnerability occurs when an application stores sensitive information, like passwords or encryption keys, in system memory that isn't properly secured from being written to disk. If the memory isn't locked, the operating system's virtual memory manager can swap it to a page or swap file, leaving the data exposed on the storage drive where attackers could potentially recover it.
To prevent sensitive data from being swapped to disk, developers use functions like `VirtualLock()` on Windows or `mlock()` on POSIX systems. However, these methods have critical limitations and platform dependencies. On older Windows versions (95, 98, Me), `VirtualLock()` is just a stub with no real effect. On POSIX systems, while `mlock()` keeps pages in physical memory, it doesn't universally guarantee they won't also appear in swap, making it an unreliable safeguard for secrets. Furthermore, using `mlock()` typically requires elevated privileges, and its behavior can vary significantly between operating systems. Developers must always check the return values of these locking functions to confirm they succeeded, as a silent failure leaves data unprotected. Crucially, relying solely on memory locking is a fragile strategy. A more secure approach involves avoiding long-term storage of sensitive data in memory altogether, using secure, dedicated functions provided by the operating system for handling secrets, or encrypting the data before it ever touches volatile memory.
Real-world impact

Real-world CVEs caused by CWE-591

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-591

  • Architecture and Design Identify data that needs to be protected from swapping and choose platform-appropriate protection mechanisms.
  • Implementation Check return values to ensure locking operations are successful.
Detection signals

How to detect CWE-591

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-591 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.

Get a demo Try Plexicus free
Frequently asked questions

Frequently asked questions

What is CWE-591?

This vulnerability occurs when an application stores sensitive information, like passwords or encryption keys, in system memory that isn't properly secured from being written to disk. If the memory isn't locked, the operating system's virtual memory manager can swap it to a page or swap file, leaving the data exposed on the storage drive where attackers could potentially recover it.

How serious is CWE-591?

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-591?

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

How can I prevent CWE-591?

Identify data that needs to be protected from swapping and choose platform-appropriate protection mechanisms. Check return values to ensure locking operations are successful.

How does Plexicus detect and fix CWE-591?

Plexicus's SAST engine matches the data-flow signature for CWE-591 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-591?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/591.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-591

CWE-413 Parent

Improper Resource Locking

This vulnerability occurs when an application fails to properly lock a shared resource, such as a file or memory location, before…

Resources

Further reading

Ready when you are

Don't Let Security
Weigh You Down.

Stop choosing between AI velocity and security debt. Plexicus is the only platform that runs Vibe Coding Security and ASPM in parallel — one workflow, every codebase.