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Insecure Temporary File Creation Methods in Java

Critical
securitybest practices

What is it?​

This practice is triggered by the use of insecure methods to create temporary files, which can lead to race conditions and security vulnerabilities.

Why apply it?​

Creating temporary files in a non-atomic way can lead to serious security issues like trust boundary violations, information disclosure, and race conditions which can be exploited by attackers.

How to fix it?​

Use secure APIs that create temporary files atomically, avoiding race conditions. Ensure temporary files are created with unique and unpredictable names in non-public directories.

Examples​

Example 1:​

Negative​

This negative example uses non-atomic operations to create temporary files, leading to race conditions.

import java.io.File;
import java.io.IOException;

public class InsecureTempFileExample {
    protected void createInsecureTempDir() throws IOException {
        File tempDir;
        tempDir = File.createTempFile("myApp", ".tmp");
        tempDir.delete();  // Noncompliant
        tempDir.mkdir();   // Noncompliant
        System.out.println("Directory created at: " + tempDir.getAbsolutePath());
    }
}

Example 2:​

Positive​

This positive example uses Files.createTempDirectory which securely creates a temporary directory.

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;

public class SecureTempFileExample {
    public void createSecureTempDir() throws IOException {
        Path tempPath = Files.createTempDirectory("myApp_");
        File tempDir = tempPath.toFile();
        System.out.println("Secure temporary directory created at: " + tempDir.getAbsolutePath());
    }
}

Negative​

This negative example manually handles file permissions, which can be error-prone and insecure.

import java.io.File;
import java.io.IOException;

public class InsecureTemporaryFile {
    public void createInsecureTempFile() throws IOException {
        File tempFile = new File(System.getProperty("java.io.tmpdir"), "unsafeFile.tmp");
        if (tempFile.createNewFile()) {  // Noncompliant
            boolean setReadable = tempFile.setReadable(true, true);  // Attempt to set permissions
            boolean setWritable = tempFile.setWritable(true, true);
            System.out.println("Insecure temporary file created at: " + tempFile.getAbsolutePath());
        }
    }
}

Example 3:​

Positive​

This positive example demonstrates atomic creation of a temporary file using Files.createTempFile.

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.attribute.PosixFilePermission;
import java.util.Set;
import java.util.EnumSet;

public class SecureTemporaryFile {
    public void createSecureTempFile() throws IOException {
        Set<PosixFilePermission> perms = EnumSet.of(PosixFilePermission.OWNER_READ, 
                                                    PosixFilePermission.OWNER_WRITE);
        Path tempFilePath = Files.createTempFile("secureFile_", ".tmp", 
                                                 Files.newPosixFilePermissionsAttribute(perms));
        System.out.println("Secure temporary file created at: " + tempFilePath.toString());
    }
}