Page History

Files on multiuser systems are generally owned by a particular user. The owner of the file can determine specify which other users on the system should be allowed to access the contents of these files.

These file systems generally use a privileges and permissions model to protect file access. When a file is created, the file access permissions of the file immediately dictate who may access or operate on the file. If When a program creates a file with insufficiently restrictive access permissions, an attacker may read or modify the file before the program can modify the permissions. Consequently, files must be created with access permissions that prevent unauthorized file access.

Noncompliant Code Example

The constructors for FileOutputStream and FileWriter do not allow the programmer to explicitly specify file access permissions. In this noncompliant code example, the access permissions of any file created is are implementation-defined and may fail to not prevent unauthorized access.:

Writer out = new FileWriter("file");

Compliant Solution (Java 1.6 and Earlier)

Java 1.6 and earlier provide no lack a mechanism for specifying default permissions upon file creation. Consequently, the problem must be avoided or solved using some mechanism external to Java, such as by using native code and the Java Native Interface (JNI).

Compliant Solution (

...

POSIX)

The Java 1.7 new The  I/O facility (java.nio) provides classes for managing file access permissions. Additionally, many of the methods and constructors that create files accept an argument allowing the program to specify the initial file permissions.

The Files.newByteChannel() method allows a file to be created with specific permissions. This method is platform-independent, but the actual permissions are platform-specific. The following This compliant solution shows defines sufficiently restrictive permissions for POSIX platforms.:

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)) {
  // writeWrite data
};

Exceptions

FIO03FIO01-J-EX0: If When a file is created inside a directory that is both secure and unreadable by untrusted users, then that file may be created with the default access permissions. See FIO07-J. Remove temporary files before termination for the definition of a secure directory. 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-JFIO03-EX1: Files that do not contain sensitive privileged information need not be created with specific access permissions.

Risk Assessment

The ability to determine if an existing file has been opened or a new file has been created provides greater assurance that a file other than the intended file is not acted uponIf 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

...

Tool	Version	Checker	Description
CodeSonar	Include Page CodeSonar_V CodeSonar_V	JAVA.IO.PERM.ACCESS JAVA.IO.PERM	Accessing file in permissive mode Permissive file mode
Parasoft Jtest	Include Page Parasoft_V Parasoft_V	CERT.FIO01.ASNF CERT.FIO01.CFAP	Avoid implicit file creation when a String is passed as an argument Create files with appropriate access permissions
PVS-Studio	Include Page PVS-Studio_V PVS-Studio_V	V5318

Related Guidelines

Bibliography

Android Implementation Details

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

Bibliography

...

FIO02-J. Ensure the array is filled when using read() to fill an array      12. Input Output (FIO)      void FIO04-J. Do not operate on files in shared directoriesImage Added Image Added Image Added