CWE-616: Incomplete Identification of Uploaded File Variables (PHP)
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.
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".
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Relevant to the view "Research Concepts" (CWE-1000)
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PHP (Undetermined Prevalence)
This table specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
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):
Example Language: 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
"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."
Example Language: 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.
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