CWE-378: Creation of Temporary File With Insecure Permissions

Description

Opening temporary files without appropriate measures or controls can leave the file, its contents and any function that it impacts vulnerable to attack.

Potential Impact

Confidentiality

Read Application Data

Authorization, Other

Other

Integrity, Other

Other

Demonstrative Examples

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.

Bad

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

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.

Bad

try {File temp = File.createTempFile("pattern", ".suffix");temp.deleteOnExit();BufferedWriter out = new BufferedWriter(new FileWriter(temp));out.write("aString");out.close();}catch (IOException e) {}

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.

Mitigations & Prevention

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 Methods

Automated Static Analysis — Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then sea

Real-World CVE Examples

CVE ID	Description
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

Taxonomy Mappings

CLASP: — Improper temp file opening

Frequently Asked Questions

What is CWE-378?

CWE-378 (Creation of Temporary File With Insecure Permissions) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. Opening temporary files without appropriate measures or controls can leave the file, its contents and any function that it impacts vulnerable to attack.

How can CWE-378 be exploited?

Attackers can exploit CWE-378 (Creation of Temporary File With Insecure Permissions) to read application data. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-378?

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

What is the severity of CWE-378?

CWE-378 is classified as a Base-level weakness (Medium abstraction). It has been observed in 1 real-world CVEs.