CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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ID

CWE-616: Incomplete Identification of Uploaded File Variables (PHP)

Weakness ID: 616
Abstraction: Variant
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
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".
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
NatureTypeIDName
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More general than a Base weakness.345Insufficient Verification of Data Authenticity
PeerOfVariantVariant - a weakness that is described at a very low level of detail, typically limited to a specific language or technology. More specific than a Base weakness.473PHP External Variable Modification
+ Relevant to the view "Development Concepts" (CWE-699)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.429Handler Errors
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

PhaseNote
Implementation
+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

PHP (Undetermined Prevalence)

+ Common Consequences

The table below 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.

ScopeImpactLikelihood
Confidentiality
Integrity

Technical Impact: Read Files or Directories; Modify Files or Directories

+ 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)
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

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)
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.

+ Observed Examples
ReferenceDescription
Forum does not properly verify whether a file was uploaded or if the associated variables were set by POST, allowing remote attackers to read arbitrary files.
Product doesn't check if the variables for an upload were set by uploading the file, or other methods such as $_POST.
Product does not distinguish uploaded file from other files.
+ Potential Mitigations

Phase: Architecture and Design

Use PHP 4 or later.

Phase: 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']))

Phase: Implementation

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
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
+ Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.994SFP Secondary Cluster: Tainted Input to Variable
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERIncomplete Identification of Uploaded File Variables (PHP)
Software Fault PatternsSFP25Tainted input to variable
+ References
[REF-502] Shaun Clowes. "A Study in Scarlet - section 5, "File Upload"".
+ Content History
Submissions
Submission DateSubmitterOrganization
PLOVER
Modifications
Modification DateModifierOrganization
2008-07-01Eric DalciCigital
updated Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Relationships, Observed_Example, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities
2008-10-14CWE Content TeamMITRE
updated Description, Other_Notes, Potential_Mitigations
2011-03-29CWE Content TeamMITRE
updated Other_Notes
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2012-05-11CWE Content TeamMITRE
updated Observed_Examples, Relationships
2012-10-30CWE Content TeamMITRE
updated Potential_Mitigations
2014-07-30CWE Content TeamMITRE
updated Relationships, Taxonomy_Mappings

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Page Last Updated: March 29, 2018