CWE-616 Variante Incompleto

Incomplete Identification of Uploaded File Variables (PHP)

Definição

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the automatic creation of these global variables ('register_globals' is off by default), making this a legacy issue for outdated codebases.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 no 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.

Como os atacantes a exploram

Trajeto do atacante passo a passo

1
As of 2006, the "four globals" method is probably in sharp decline, but older PHP applications could have this issue.
2
In the "four globals" method, PHP sets the following 4 global variables (where "varname" is application-dependent):
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
** note: 'userfile' is the field name from the web form; this can vary.

Exemplo de código vulnerável

Vulnerable PHP

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

Vulnerável 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

Exemplo 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 verificação de prevenção

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.

Sinais de deteção

How to detect CWE-616

SAST High

Executar análise estática (SAST) na base de código à procura do padrão inseguro no fluxo de dados.

DAST Moderate

Executar testes dinâmicos de segurança de aplicações (DAST) contra o endpoint em execução.

Runtime Moderate

Monitorizar os registos em tempo de execução para traços de exceção invulgares, input malformado ou tentativas de contornar a autorização.

Code review Moderate

Revisão de código: sinalizar qualquer novo código que trate input desta superfície sem usar os ajudantes validados do framework.

Correção automática do Plexicus

O Plexicus deteta automaticamente o CWE-616 e abre um PR de correção em menos de 60 segundos.

O Codex Remedium analisa cada commit, identifica esta fraqueza exata e entrega um pull request pronto para revisão com o patch. Sem tickets. Sem transferências.

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Perguntas frequentes

Frequently asked questions

O que é o CWE-616?

Qual a gravidade do CWE-616?

A MITRE não publicou uma classificação de probabilidade de exploração para esta fraqueza. Trate-a como impacto médio até o seu modelo de ameaças provar o contrário.

Que linguagens ou plataformas são afetadas pelo CWE-616?

MITRE lists the following affected platforms: PHP.

Como posso prevenir o 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']))

Como é que o Plexicus deteta e corrige o CWE-616?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-616 em cada commit. Quando é encontrada uma correspondência, o nosso agente Codex Remedium abre um PR de correção com o código corrigido, testes e um resumo de uma linha para o revisor.

Onde posso saber mais sobre o CWE-616?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/616.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

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