CWE-616 Variante Incompleto

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…

Definición

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the automatic creation of these global variables ('register_globals' is off by default), making this a legacy issue for outdated codebases.
Impacto en el mundo real

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.

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

  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.

Ejemplo de código vulnerable

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
Ejemplo de código seguro

Secure pseudo

Seguro 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.
Lista de prevención

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.
Señales de detección

How to detect CWE-616

SAST High

Ejecuta análisis estático (SAST) sobre el código buscando el patrón inseguro en el flujo de datos.

DAST Moderate

Ejecuta pruebas dinámicas de seguridad de aplicaciones (DAST) contra el endpoint en vivo.

Runtime Moderate

Vigila los logs en tiempo de ejecución para detectar trazas de excepción inusuales, entradas malformadas o intentos de bypass de autorización.

Code review Moderate

Revisión de código: marca cualquier código nuevo que maneje entrada desde esta superficie sin usar los helpers validados del framework.

Auto-corrección de Plexicus

Plexicus detecta automáticamente CWE-616 y abre un PR de corrección en menos de 60 segundos.

Codex Remedium escanea cada commit, identifica esta debilidad concreta y entrega un pull request listo para revisión con el parche. Sin tickets. Sin traspasos.

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Preguntas frecuentes

Frequently asked questions

¿Qué es 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.

¿Qué gravedad tiene CWE-616?

MITRE no ha publicado una calificación de probabilidad de explotación para esta debilidad. Trátala como de impacto medio hasta que tu modelo de amenazas demuestre lo contrario.

¿Qué lenguajes o plataformas se ven afectados por CWE-616?

MITRE lists the following affected platforms: PHP.

¿Cómo puedo prevenir 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']))

¿Cómo detecta y corrige Plexicus CWE-616?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-616 en cada commit. Cuando hay coincidencia, nuestro agente Codex Remedium abre un PR de corrección con el código corregido, las pruebas y un resumen de una línea para el revisor.

¿Dónde puedo aprender más sobre CWE-616?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/616.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-616

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Recursos

Further reading

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