CWE-689 Compound Draft

Permission Race Condition During Resource Copy

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation is finished. During the copy process, the resource remains…

Definition

What is CWE-689?

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation is finished. During the copy process, the resource remains exposed with default or overly permissive access, creating a temporary window where unauthorized users or processes could read, modify, or delete it.
This race condition is a classic time-of-check to time-of-use (TOCTOU) flaw specific to resource duplication. When an application copies a file—for example, during installation, backup, or user upload—it often creates the new file with broad default permissions (like world-readable) to ensure the copy succeeds. The intended restrictive permissions are only applied after the data transfer is complete. This gap, however brief, is a real security risk, especially on multi-user systems or shared hosting environments where other processes are actively running. To prevent this, developers should implement atomic operations where possible, such as creating the file with the correct permissions from the outset before writing data. Alternatively, copy operations can be performed in a secure, isolated temporary location with strict access controls, and the file should only be moved to its final destination after both the data and the correct permissions are fully applied, eliminating the exposure window.
Real-world impact

Real-world CVEs caused by CWE-689

  • CVE-2002-0760

    Archive extractor decompresses files with world-readable permissions, then later sets permissions to what the archive specified.

  • CVE-2005-2174

    Product inserts a new object into database before setting the object's permissions, introducing a race condition.

  • CVE-2006-5214

    Error file has weak permissions before a chmod is performed.

  • CVE-2005-2475

    Archive permissions issue using hard link.

  • CVE-2003-0265

    Database product creates files world-writable before initializing the setuid bits, leading to modification of executables.

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-689

  • 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-689

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-689 and opens a fix PR in under 60 seconds.

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Frequently asked questions

Frequently asked questions

What is CWE-689?

This vulnerability occurs when a system copies a file or resource but delays setting its final permissions until the entire copy operation is finished. During the copy process, the resource remains exposed with default or overly permissive access, creating a temporary window where unauthorized users or processes could read, modify, or delete it.

How serious is CWE-689?

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-689?

MITRE lists the following affected platforms: C, Perl.

How can I prevent CWE-689?

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-689?

Plexicus's SAST engine matches the data-flow signature for CWE-689 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-689?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/689.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-689

CWE-362 Parent

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

A race condition occurs when multiple processes or threads access a shared resource simultaneously without proper coordination, creating a…

CWE-1223 Sibling

Race Condition for Write-Once Attributes

This vulnerability occurs when an untrusted software component wins a race condition and writes to a hardware register before the trusted…

CWE-1298 Sibling

Hardware Logic Contains Race Conditions

A hardware race condition occurs when security-critical logic circuits receive signals at slightly different times, creating temporary…

CWE-364 Sibling

Signal Handler Race Condition

A signal handler race condition occurs when a program's signal handling routine is vulnerable to timing issues, allowing its state to be…

CWE-366 Sibling

Race Condition within a Thread

This vulnerability occurs when two or more threads within the same application access and manipulate a shared resource (like a variable,…

CWE-367 Sibling

Time-of-check Time-of-use (TOCTOU) Race Condition

This vulnerability occurs when a program verifies a resource's state (like a file's permissions or existence) but then uses it after that…

CWE-368 Sibling

Context Switching Race Condition

This vulnerability occurs when an application switches between different security contexts (like privilege levels or domains) using a…

CWE-421 Sibling

Race Condition During Access to Alternate Channel

A race condition occurs when an application opens a secondary communication channel intended for an authorized user, but fails to secure…

CWE-732 Peer

Incorrect Permission Assignment for Critical Resource

This vulnerability occurs when a system grants overly permissive access to a sensitive resource, allowing unauthorized users or processes…

Resources

Further reading

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