CWE-910 Base Incomplete Medium likelihood

Use of Expired File Descriptor

This vulnerability occurs when a program attempts to use a file descriptor after it has been closed, treating it as if it were still valid.

Definition

What is CWE-910?

This vulnerability occurs when a program attempts to use a file descriptor after it has been closed, treating it as if it were still valid.
When a file descriptor is closed, the operating system marks it as available for reuse. If your code later uses that same descriptor value—thinking it still points to the original file or socket—it will actually be interacting with a completely different, newly opened resource. This can lead to data corruption, security breaches, or application crashes as you read from or write to an unintended target. To prevent this, developers should immediately set file descriptor variables to an invalid state (like -1) after closing them and implement robust state checks before use. Relying on the descriptor value alone is unsafe because the system recycles these identifiers, breaking the assumed link between the descriptor number and your intended resource.
Real-world impact

Real-world CVEs caused by CWE-910

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-910

  • 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-910

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-910 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-910?

This vulnerability occurs when a program attempts to use a file descriptor after it has been closed, treating it as if it were still valid.

How serious is CWE-910?

MITRE rates the likelihood of exploit as Medium — exploitation is realistic but typically requires specific conditions.

What languages or platforms are affected by CWE-910?

MITRE lists the following affected platforms: C, C++.

How can I prevent CWE-910?

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-910?

Plexicus's SAST engine matches the data-flow signature for CWE-910 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-910?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/910.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-910

CWE-672 Parent

Operation on a Resource after Expiration or Release

This vulnerability occurs when a program continues to use a resource—like memory, a file handle, or a network connection—after it has been…

CWE-298 Sibling

Improper Validation of Certificate Expiration

This vulnerability occurs when an application fails to properly check if a digital certificate has expired, potentially trusting…

CWE-324 Sibling

Use of a Key Past its Expiration Date

This vulnerability occurs when an application continues to use a cryptographic key or password after its designated expiration date. Doing…

CWE-415 Sibling

Double Free

A double free vulnerability occurs when a program mistakenly calls the 'free()' function twice on the same block of memory.

CWE-416 Sibling

Use After Free

Use After Free happens when a program continues to use a pointer to a memory location after that memory has been freed. This can lead to…

CWE-613 Sibling

Insufficient Session Expiration

Insufficient session expiration occurs when an application allows old session tokens or IDs to remain valid for too long, letting…

CWE-825 Sibling

Expired Pointer Dereference

This vulnerability occurs when a program tries to use a pointer that still points to a memory location that has already been freed or…

Resources

Further reading

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