Creation of Temporary File in Directory with Insecure Permissions

Incomplete Base

Structure: Simple

Description

This vulnerability occurs when an application creates a temporary file in a directory that is too permissive, allowing unauthorized users or processes to see, access, or manipulate the file.

Extended Description

When a temporary file is placed in a directory with loose permissions (like world-readable or world-writable), other users or system actors can detect its presence. This simple act of discovery reveals which application created the file, offering a window into what the user is currently doing. Attackers can correlate this information with running processes to infer sensitive user activity, turning a seemingly minor information leak into a serious privacy breach. This issue is more than just a file access problem; it's an information exposure flaw that can enable targeted attacks. By knowing which application is in use, an attacker gains critical context to craft further exploits, potentially escalating privileges or accessing confidential data. Developers must ensure temporary files are created in secure, private locations with strict access controls to prevent this form of reconnaissance.

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