Creation of Temporary File With Insecure Permissions

Draft Base

Structure: Simple

Description

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.

Extended Description

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.

Common Consequences 3

Scope: Confidentiality

Impact: Read Application Data

If the temporary file can be read by the attacker, sensitive information may be in that file which could be revealed.

Scope: AuthorizationOther

Impact: Other

If that file can be written to by the attacker, the file might be moved into a place to which the attacker does not have access. This will allow the attacker to gain selective resource access-control privileges.

Scope: IntegrityOther

Impact: Other

Depending on the data stored in the temporary file, there is the potential for an attacker to gain an additional input vector which is trusted as non-malicious. It may be possible to make arbitrary changes to data structures, user information, or even process ownership.

Potential Mitigations 3

Phase: Requirements

Many contemporary languages have functions which properly handle this condition. Older C temp file functions are especially susceptible.

Phase: 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.

Phase: 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.

Demonstrative Examples 1

ID : DX-139

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.

Code Example:

Bad

// write data to tmp file* ... // remove tmp file rmtmp();

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.

Code Example:Bad
Java
java

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

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.

Observed Examples 1

CVE-2022-24823A network application framework uses the Java function createTempFile(), which will create a file that is readable by other local users of the system

References 1

The CLASP Application Security Process

Secure Software, Inc.

2005

https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf(2024-11-17)

ID: REF-18

Likelihood of Exploit

High

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Insecure Temporary File (CWE-377)

Taxonomy Mapping

CLASP