Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
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
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 pseudo
MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.
// 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
// 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
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-591
Don't catalog this weakness. Prove it's reachable.
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Frequently asked questions What is CWE-591?
How serious is CWE-591?
What languages or platforms are affected by CWE-591?
How can I prevent CWE-591?
How does Plexicus detect and fix CWE-591?
Where can I learn more about CWE-591?
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
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