CWE-616 Variant Incomplete

Incomplete Identification of Uploaded File Variables (PHP)

This vulnerability occurs in PHP applications that rely on the deprecated, auto-registered global variables for file uploads (like $varname, $varname_size). Because these variables are not properly…

Definition

What is CWE-616?

This vulnerability occurs in PHP applications that rely on the deprecated, auto-registered global variables for file uploads (like $varname, $varname_size). Because these variables are not properly validated, an attacker can overwrite them to trick the application into processing malicious or unauthorized files.
In older PHP configurations, file uploads automatically created a set of global variables for each file. Attackers can exploit this by sending forged POST requests or manipulated cookies that overwrite these variables with their own values. Since the application trusts these globals without verification, it can be deceived into handling files it was never intended to, such as sensitive system files. To prevent this, developers must stop using these legacy global variables entirely. The secure alternative is to use the validated $_FILES superglobal array, which is populated directly by the PHP engine and is immune to this type of user-supplied data overwrite. Modern PHP versions have disabled the automatic creation of these global variables ('register_globals' is off by default), making this a legacy issue for outdated codebases.
Real-world impact

Real-world CVEs caused by CWE-616

  • CVE-2002-1460

    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.

  • CVE-2002-1759

    Product doesn't check if the variables for an upload were set by uploading the file, or other methods such as $_POST.

  • CVE-2002-1710

    Product does not distinguish uploaded file from other files.

How attackers exploit it

Step-by-step attacker path

  1. 1

    As of 2006, the "four globals" method is probably in sharp decline, but older PHP applications could have this issue.

  2. 2

    In the "four globals" method, PHP sets the following 4 global variables (where "varname" is application-dependent):

  3. 3

    "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."

  4. 4

    ** note: 'userfile' is the field name from the web form; this can vary.

Vulnerable code example

Vulnerable PHP

In the "four globals" method, PHP sets the following 4 global variables (where "varname" is application-dependent):

Vulnerable 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
Secure code example

Secure pseudo

Secure pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-616

  • 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']))
  • 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.
Detection signals

How to detect CWE-616

SAST High

Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.

DAST Moderate

Run dynamic application security testing against the live endpoint.

Runtime Moderate

Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.

Code review Moderate

Code review: flag any new code that handles input from this surface without using the validated framework helpers.

Plexicus auto-fix

Plexicus auto-detects CWE-616 and opens a fix PR in under 60 seconds.

Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.

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Frequently asked questions

Frequently asked questions

What is CWE-616?

This vulnerability occurs in PHP applications that rely on the deprecated, auto-registered global variables for file uploads (like $varname, $varname_size). Because these variables are not properly validated, an attacker can overwrite them to trick the application into processing malicious or unauthorized files.

How serious is CWE-616?

MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.

What languages or platforms are affected by CWE-616?

MITRE lists the following affected platforms: PHP.

How can I prevent CWE-616?

Use PHP 4 or later. If you must support older PHP versions, write your own version of is_uploaded_file() and run it against $HTTP_POST_FILES['userfile']))

How does Plexicus detect and fix CWE-616?

Plexicus's SAST engine matches the data-flow signature for CWE-616 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-616?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/616.html. You can also reference OWASP and NIST documentation for adjacent guidance.

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