CWE-616: Incomplete Identification of Uploaded File Variables (PHP)
Incomplete Identification of Uploaded File Variables (PHP)
Weakness ID: 616 (Weakness Variant)
Status: Incomplete
Description
Description Summary
The PHP application uses an old method for processing uploaded
files by referencing the four global variables that are set for each file (e.g.
$varname, $varname_size, $varname_name, $varname_type). These variables could be
overwritten by attackers, causing the application to process unauthorized
files.
Extended Description
These global variables could be overwritten by POST requests, cookies, or
other methods of populating or overwriting these variables This could be
used to read or process arbitrary files by providing values such as
"/etc/passwd".
Time of Introduction
Implementation
Applicable Platforms
Languages
PHP
Demonstrative Examples
Example 1
As of 2006, the "four globals" method is probably in sharp decline,
but older PHP applications could have this issue.
In the "four globals" method, PHP sets the following 4 global
variables (where "varname" is application-dependent):
(Bad Code)
PHP
$varname = name of the temporary file on local machine
$varname_size = size of file
$varname_name = original name of file provided by client
$varname_type = MIME type of the file
Example 2
"The global $_FILES exists as of PHP 4.1.0 (Use $HTTP_POST_FILES
instead if using an earlier version). These arrays will contain all the
uploaded file information."
(Bad Code)
PHP
$_FILES['userfile']['name'] - original filename from client
$_FILES['userfile']['tmp_name'] - the temp filename of the file on
the server
** note: 'userfile' is the field name from the web form; this can
vary.
PHP script does not restrict access to uploaded
files. Overlaps container error.
Potential Mitigations
Phase
Description
Architecture and Design
Use PHP 4 or later.
Architecture and Design
If you must support older PHP versions, write your own version of
is_uploaded_file() and run it against
$HTTP_POST_FILES['userfile']))
For later PHP versions, reference uploaded files using the
$HTTP_POST_FILES or $_FILES variables, and use is_uploaded_file() or
move_uploaded_file() to ensure that you are dealing with an uploaded
file.
Weakness Ordinalities
Ordinality
Description
Primary
(where the
weakness exists independent of other weaknesses)
Description
