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CWE-473 Variante Rascunho
PHP External Variable Modification
This vulnerability occurs when a PHP application fails to properly validate or sanitize variables that originate from outside the application, such as HTTP query strings, cookies, or POST data.…
Definição
What is CWE-473?
This vulnerability occurs when a PHP application fails to properly validate or sanitize variables that originate from outside the application, such as HTTP query strings, cookies, or POST data. Attackers can exploit this to inject unexpected values, altering the program's logic and security controls.
PHP's historical feature of automatically registering global variables from user input (like `$_GET`, `$_POST`) created a major security pitfall. Even with this feature deprecated, the core risk remains: if developers directly trust external data without validation, attackers can overwrite critical internal variables. This opens the door to authentication bypass, privilege escalation, or logic flaws that shouldn't exist in a properly isolated codebase.
To prevent this, developers must adopt a clear separation between external input and internal application state. Always initialize variables explicitly, disable legacy features like `register_globals`, and treat all user-supplied data as untrusted. Implement strict validation and use allow-lists for expected values, ensuring external sources cannot arbitrarily modify the variables that control your application's behavior and security decisions.
Impacto no mundo real
Real-world CVEs caused by CWE-473
-
File upload allows arbitrary file read by setting hidden form variables to match internal variable names.
-
Mistakenly trusts $PHP_SELF variable to determine if include script was called by its parent.
-
PHP remote file inclusion by modified assumed-immutable variable.
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Modify key variable when calling scripts that don't load a library that initializes it.
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Authentication bypass by modifying array used for authentication.
Como os atacantes a exploram
Trajeto do atacante passo a passo
- 1
Identificar um caminho de código que trata input não confiável sem validação.
- 2
Criar um payload que explora o comportamento inseguro — injeção, traversal, overflow ou abuso de lógica.
- 3
Entregar o payload através de um pedido normal e observar a reação da aplicação.
- 4
Iterar até que a resposta exponha dados, execute código do atacante ou escale privilégios.
Exemplo de código vulnerável
Vulnerable pseudo
A MITRE não publicou um exemplo de código para este CWE. O padrão abaixo é ilustrativo — consulte os Recursos para referências canónicas.
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
// Untrusted input flows directly into the sensitive sink.
return executeUnsafe(input);
} Exemplo de código seguro
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.
Lista de verificação de prevenção
How to prevent CWE-473
- Requirements / Implementation Carefully identify which variables can be controlled or influenced by an external user, and consider adopting a naming convention to emphasize when externally modifiable variables are being used. An application should be reluctant to trust variables that have been initialized outside of its trust boundary. Ensure adequate checking is performed when relying on input from outside a trust boundary. Do not allow your application to run with register_globals enabled. If you implement a register_globals emulator, be extremely careful of variable extraction, dynamic evaluation, and similar issues, since weaknesses in your emulation could allow external variable modification to take place even without register_globals.
Sinais de deteção
How to detect CWE-473
Executar testes dinâmicos de segurança de aplicações (DAST) contra o endpoint em execução.
Monitorizar os registos em tempo de execução para traços de exceção invulgares, input malformado ou tentativas de contornar a autorização.
Revisão de código: sinalizar qualquer novo código que trate input desta superfície sem usar os ajudantes validados do framework.
CWE-473
Don't catalog this weakness. Prove it's reachable.
Plexicus turns CWE catalogs into evidence: every CWE-pattern is matched against your real code graph, reach is proven on a sandbox clone, and verified findings ship as reviewed PRs.
Perguntas frequentes O que é o CWE-473?
Qual a gravidade do CWE-473?
Que linguagens ou plataformas são afetadas pelo CWE-473?
Como posso prevenir o CWE-473?
Como é que o Plexicus deteta e corrige o CWE-473?
Onde posso saber mais sobre o CWE-473?
Frequently asked questions
O que é o CWE-473?
This vulnerability occurs when a PHP application fails to properly validate or sanitize variables that originate from outside the application, such as HTTP query strings, cookies, or POST data. Attackers can exploit this to inject unexpected values, altering the program's logic and security controls.
Qual a gravidade do CWE-473?
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-473?
MITRE lists the following affected platforms: PHP.
Como posso prevenir o CWE-473?
Carefully identify which variables can be controlled or influenced by an external user, and consider adopting a naming convention to emphasize when externally modifiable variables are being used. An application should be reluctant to trust variables that have been initialized outside of its trust boundary. Ensure adequate checking is performed when relying on input from outside a trust boundary. Do not allow your application to run with register_globals enabled. If you implement a…
Como é que o Plexicus deteta e corrige o CWE-473?
O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-473 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-473?
A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/473.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.
Fraquezas relacionadas
Weaknesses related to CWE-473
CWE-471 Pai
Modification of Assumed-Immutable Data (MAID)
This vulnerability occurs when an application fails to protect data it assumes cannot be changed, allowing an attacker to alter it.
CWE-472 Irmão
External Control of Assumed-Immutable Web Parameter
This vulnerability occurs when a web application incorrectly trusts data that appears to be fixed or hidden from the user, such as values…
CWE-607 Irmão
Public Static Final Field References Mutable Object
This vulnerability occurs when a class exposes a public or protected static final field that points to a changeable object. Because the…
CWE-98 Pode preceder
Improper Control of Filename for Include/Require Statement in PHP Program ('PHP Remote File Inclusion')
This vulnerability occurs when a PHP application uses unvalidated or insufficiently restricted user input directly within file inclusion…
Pronto para validar o que importa?
Pronto para validar o que importa.
O Plexicus é Proof-Driven AppSec: achados validados, compreensão contextual e remediação revisada — ancorada em evidência, escopada com você.