CWE-378 Base Draft High likelihood

Creation of Temporary File With Insecure Permissions

This vulnerability occurs when a program creates a temporary file but sets its file permissions too loosely, allowing other users or processes on the system to read, modify, or delete the file.

Definition

What is CWE-378?

This vulnerability occurs when a program creates a temporary file but sets its file permissions too loosely, allowing other users or processes on the system to read, modify, or delete the file.
When a temporary file is created with insecure permissions (like world-readable or world-writable), it becomes an easy target for attackers on the same system. They can directly read sensitive data from the file, inject malicious content into it, or even delete it to cause a denial of service. This is especially dangerous because developers often assume temporary files are private and secure, leading them to store sensitive information like session tokens, passwords, or configuration data in them. To prevent this, always use secure APIs designed for temporary file creation that enforce strict permissions by default, such as `mkstemp` on Unix-like systems. If you must use a lower-level function, explicitly set restrictive file permissions immediately after creation. Additionally, consider using alternative, more secure storage methods like memory-based structures for highly sensitive data, and ensure proper file cleanup to reduce the attack window.
Real-world impact

Real-world CVEs caused by CWE-378

  • CVE-2022-24823

    A network application framework uses the Java function createTempFile(), which will create a file that is readable by other local users of the system

How attackers exploit it

Step-by-step attacker path

  1. 1

    In the following code examples a temporary file is created and written to. After using the temporary file, the file is closed and deleted from the file system.

  2. 2

    However, within this C/C++ code the method tmpfile() is used to create and open the temp file. The tmpfile() method works the same way as the fopen() method would with read/write permission, allowing attackers to read potentially sensitive information contained in the temp file or modify the contents of the file.

  3. 3

    Similarly, the createTempFile() method used in the Java code creates a temp file that may be readable and writable to all users.

  4. 4

    Additionally both methods used above place the file into a default directory. On UNIX systems the default directory is usually "/tmp" or "/var/tmp" and on Windows systems the default directory is usually "C:\\Windows\\Temp", which may be easily accessible to attackers, possibly enabling them to read and modify the contents of the temp file.

Vulnerable code example

Vulnerable C

In the following code examples a temporary file is created and written to. After using the temporary file, the file is closed and deleted from the file system.

Vulnerable C 
FILE *stream;
  if( (stream = tmpfile()) == NULL ) {
  		perror("Could not open new temporary file\n");
  		return (-1);
  }
```
// write data to tmp file* 
  ...
  // remove tmp file
  rmtmp();
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-378

  • Requirements Many contemporary languages have functions which properly handle this condition. Older C temp file functions are especially susceptible.
  • Implementation Ensure that you use proper file permissions. This can be achieved by using a safe temp file function. Temporary files should be writable and readable only by the process that owns the file.
  • Implementation Randomize temporary file names. This can also be achieved by using a safe temp-file function. This will ensure that temporary files will not be created in predictable places.
Detection signals

How to detect CWE-378

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-378 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-378?

This vulnerability occurs when a program creates a temporary file but sets its file permissions too loosely, allowing other users or processes on the system to read, modify, or delete the file.

How serious is CWE-378?

MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.

What languages or platforms are affected by CWE-378?

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

How can I prevent CWE-378?

Many contemporary languages have functions which properly handle this condition. Older C temp file functions are especially susceptible. Ensure that you use proper file permissions. This can be achieved by using a safe temp file function. Temporary files should be writable and readable only by the process that owns the file.

How does Plexicus detect and fix CWE-378?

Plexicus's SAST engine matches the data-flow signature for CWE-378 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-378?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/378.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-378

CWE-377 Parent

Insecure Temporary File

This vulnerability occurs when an application creates temporary files with insecure permissions or in predictable locations, allowing…

CWE-379 Sibling

Creation of Temporary File in Directory with Insecure Permissions

This vulnerability occurs when an application creates a temporary file in a directory that is too permissive, allowing unauthorized users…

Resources

Further reading

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