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Path file = new File("file").toPath();

// Throw exception rather than overwrite existing file
Set<OpenOption> options = new HashSet<OpenOption>();
options.add(StandardOpenOption.CREATE_NEW);
options.add(StandardOpenOption.APPEND);

// File permissions should be such that only user may read/write file
Set<PosixFilePermission> perms =
    PosixFilePermissions.fromString("rw-------");
FileAttribute<Set<PosixFilePermission>> attr =
    PosixFilePermissions.asFileAttribute(perms);

try (SeekableByteChannel sbc =
         Files.newByteChannel(file, options, attr)) {
  // Write data
};

Exceptions

FIO01-J-EX0: When a file is created inside a directory that is both secure and unreadable by untrusted users, that file may be created with the default access permissions. This could be the case if, for example, the entire file system is trusted or is accessible only to trusted users (see FIO00-J. Do not operate on files in shared directories for the definition of a secure directory).

FIO01-J-EX1: Files that do not contain privileged information need not be created with specific access permissions.

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If files are created without appropriate permissions, an attacker may read or write to the files, possibly resulting in compromised system integrity and information disclosure.

Automated Detection

Related Guidelines

Android Implementation Details

Creating files with weak permissions may allow malicious applications to access the files.

Bibliography

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