Creation of Temporary File in Directory with Insecure Permissions

The software creates a temporary file in a directory whose permissions allow unintended actors to determine the file's existence or otherwise access that file.


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.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

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.

FILE *stream;
if( (stream = tmpfile()) == NULL ) {


  perror("Could not open new temporary file\n");
  return (-1);

}
// 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.

try {
  File temp = File.createTempFile("pattern", ".suffix");
  temp.deleteOnExit();
  BufferedWriter out = new BufferedWriter(new FileWriter(temp));
  out.write("aString");
  out.close();
}
catch (IOException e) {
}

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.

See Also

File Handling Issues

Weaknesses in this category are related to the handling of files within a software system. Files, directories, and folders are so central to information technology tha...

SFP Secondary Cluster: Exposure Temporary File

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CERT C++ Secure Coding Section 09 - Input Output (FIO)

Weaknesses in this category are related to rules in the Input Output (FIO) section of the CERT C++ Secure Coding Standard. Since not all rules map to specific weakness...

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.


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