Creation of Temporary File in Directory with Insecure Permissions

Incomplete Base

Structure: Simple

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.

Extended Description

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.

Common Consequences 1

Scope: Confidentiality

Impact: Read Application Data

Since the file is visible and the application which is using the temp file could be known, the attacker has gained information about what the user is doing at that time.

Detection Methods 1

Automated Static AnalysisHigh

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 searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

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

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

Phase: Implementation

Avoid using vulnerable temp file functions.

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 2

CVE-2022-27818A hotkey daemon written in Rust creates a domain socket file underneath /tmp, which is accessible by any user.

CVE-2021-21290A Java-based application for a rapid-development framework uses File.createTempFile() to create a random temporary file with insecure default permissions.

References 2

The CLASP Application Security Process

Secure Software, Inc.

2005

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

ID: REF-18

The Art of Software Security Assessment

Mark Dowd, John McDonald, and Justin Schuh

Addison Wesley

2006

ID: REF-62

Likelihood of Exploit

Low

Applicable Platforms

Languages:

Not Language-Specific : Undetermined

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Insecure Temporary File (CWE-377)

Taxonomy Mapping

CLASP
CERT C Secure Coding