CWE-378: Creation of Temporary File With Insecure Permissions
Creation of Temporary File With Insecure Permissions
Weakness ID: 378 (Weakness Base)
Status: Draft
Description
Description Summary
Opening temporary files without appropriate measures or
controls can leave the file, its contents and any function that it impacts
vulnerable to attack.
Time of Introduction
Architecture and Design
Implementation
Applicable Platforms
Languages
All
Common Consequences
Scope
Effect
Confidentiality
If the temporary file can be read, by the attacker, sensitive
information may be in that file which could be revealed.
Authorization
If that file can be written to by the attacker, the file might be
moved into a place to which the attacker does not have access. This will
allow the attacker to gain selective resource access-control
privileges.
Integrity
Depending on the data stored in the temporary file, there is the
potential for an attacker to gain an additional input vector which is
trusted as non-malicious. It may be possible to make arbitrary changes
to data structures, user information, or even process ownership.
Likelihood of Exploit
High
Demonstrative Examples
Example 1
(Bad Code)
C and C++
FILE *stream; char tempstring[] = "String to be written";
if( (stream = tmpfile()) == NULL ) {
perror("Could not open new temporary file\n");
return (-1);
}
/* write data to tmp file */
/* ... */
_rmtmp();
The temp file created in the above code is always readable and
writable by all users.
BufferedWriter out = new BufferedWriter(new
FileWriter(temp));
out.write("aString");
out.close();
}
catch (IOException e) {
}
This temp file is readable by all users.
Potential Mitigations
Phase
Description
Tempfile creation should be done in a safe way. To be safe, the temp
file function should open up the temp file with appropriate access
control. The temp file function should also retain this quality, while
being resistant to race conditions.
Requirements specification: Many contemporary languages have functions
which properly handle this condition. Older C temp file functions are
especially susceptible.
Implementation
Ensure that you use proper file permissions. This can be achieved by
using a safe temp file function. Temporary files should be writable and
readable only by the process which own the file.
Implementation
Randomize temporary file names. This can also be achieved by using a
safe temp-file function. This will ensure that temporary files will not
be created in predictable places.
Description
