CWE-379: Creation of Temporary File in Directory with Insecure Permissions

Description

The product creates a temporary file in a directory whose permissions allow unintended actors to determine the file's existence or otherwise access that file.

On some operating systems, the fact that the temporary file exists may be apparent to any user with sufficient privileges to access that directory. Since the file is visible, the application that is using the temporary file could be known. If one has access to list the processes on the system, the attacker has gained information about what the user is doing at that time. By correlating this with the applications the user is running, an attacker could potentially discover what a user's actions are. From this, higher levels of security could be breached.

Potential Impact

Confidentiality

Read Application Data

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

Try to store sensitive tempfiles in a directory which is not world readable -- i.e., per-user directories.

Implementation

Avoid using vulnerable temp file functions.

Detection Methods

Automated Static Analysis High — 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-2022-27818	A hotkey daemon written in Rust creates a domain socket file underneath /tmp, which is accessible by any user.
CVE-2021-41989	analytic platform's repair functionality uses the %TEMP% folder of a user while running with higher privileges
CVE-2021-21290	A Java-based application for a rapid-development framework uses File.createTempFile() to create a random temporary file with insecure default permissions.

Taxonomy Mappings

CLASP: — Guessed or visible temporary file
CERT C Secure Coding: FIO15-C — Ensure that file operations are performed in a secure directory

Frequently Asked Questions

What is CWE-379?

CWE-379 (Creation of Temporary File in Directory with Insecure Permissions) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. The product creates a temporary file in a directory whose permissions allow unintended actors to determine the file's existence or otherwise access that file.

How can CWE-379 be exploited?

Attackers can exploit CWE-379 (Creation of Temporary File in Directory with Insecure Permissions) to read application data. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-379?

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-379?

CWE-379 is classified as a Base-level weakness (Medium abstraction). It has been observed in 3 real-world CVEs.