CWE-790 Classe Incompleto

Improper Filtering of Special Elements

This vulnerability occurs when an application accepts data from a source but fails to properly sanitize or incorrectly filters out special characters or control elements before passing that data to…

Definição

What is CWE-790?

At its core, this weakness is about a broken chain of trust in data handling. An application often assumes data from an upstream component (like a user, another service, or a database) is safe, but it must actively validate and neutralize potentially dangerous elements—such as quotes, brackets, script tags, or command delimiters—before that data flows downstream. If this filtering step is missing or flawed, the downstream component interprets these special elements as part of its own commands or code, leading to security breaches. For developers, this means you cannot rely on the source of your data. You must implement context-aware filtering or encoding at the point where data is used. For example, data destined for SQL needs parameterized queries, data for HTML output needs HTML entity encoding, and data for system commands needs strict allow-list validation. The fix isn't a single filter; it's applying the correct defense for each specific output context to prevent injections, cross-site scripting (XSS), and command execution attacks.

Impacto no mundo real

Real-world CVEs caused by CWE-790

Ainda não há referências CVE públicas associadas a este CWE no catálogo da MITRE.

Como os atacantes a exploram

Trajeto do atacante passo a passo

1
The following code takes untrusted input and uses a regular expression to filter "../" from the input. It then appends this result to the /home/user/ directory and attempts to read the file in the final resulting path.
2
Since the regular expression does not have the /g global match modifier, it only removes the first instance of "../" it comes across. So an input value such as:
3
will have the first "../" stripped, resulting in:
4
This value is then concatenated with the /home/user/ directory:
5
which causes the /etc/passwd file to be retrieved once the operating system has resolved the ../ sequences in the pathname. This leads to relative path traversal (CWE-23).

Exemplo de código vulnerável

Vulnerable Perl

The following code takes untrusted input and uses a regular expression to filter "../" from the input. It then appends this result to the /home/user/ directory and attempts to read the file in the final resulting path.

Vulnerável Perl

my $Username = GetUntrustedInput();
  $Username =~ s/\.\.\///;
  my $filename = "/home/user/" . $Username;
  ReadAndSendFile($filename);

Payload do atacante

Since the regular expression does not have the /g global match modifier, it only removes the first instance of "../" it comes across. So an input value such as:

Payload do atacante

../../../etc/passwd

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-790

Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
Implementation Validate input at trust boundaries; use allowlists, not denylists.
Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
Operation Monitor logs for the runtime signals listed in the next section.

Sinais de deteção

How to detect CWE-790

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-790 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-790?

Qual a gravidade do CWE-790?

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-790?

A MITRE não especificou as plataformas afetadas por este CWE — pode aplicar-se à maioria das stacks de aplicações.

Como posso prevenir o CWE-790?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

Como é que o Plexicus deteta e corrige o CWE-790?

O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-790 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-790?

A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/790.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.

Fraquezas relacionadas

Weaknesses related to CWE-790

CWE-138 Pai

Improper Neutralization of Special Elements

This vulnerability occurs when an application accepts external input but fails to properly sanitize special characters or syntax that have…

CWE-140 Irmão

Improper Neutralization of Delimiters

This vulnerability occurs when an application fails to properly handle or sanitize delimiter characters within data inputs, allowing them…

CWE-147 Irmão

Improper Neutralization of Input Terminators

This vulnerability occurs when an application accepts external input but fails to properly handle special characters that downstream…

CWE-148 Irmão

Improper Neutralization of Input Leaders

This vulnerability occurs when an application fails to properly validate or handle input that begins with special control characters or…

CWE-149 Irmão

Improper Neutralization of Quoting Syntax

This vulnerability occurs when an application fails to properly validate or escape quote characters (like single ' or double " quotes) in…

CWE-150 Irmão

Improper Neutralization of Escape, Meta, or Control Sequences

This vulnerability occurs when an application fails to properly sanitize or escape special character sequences in user-supplied input…

CWE-151 Irmão

Improper Neutralization of Comment Delimiters

This vulnerability occurs when an application accepts user input and fails to properly sanitize characters that can be interpreted as…

CWE-152 Irmão

Improper Neutralization of Macro Symbols

This vulnerability occurs when an application accepts user input containing macro symbols (like those used in templates or configuration…

CWE-153 Irmão

Improper Neutralization of Substitution Characters

This vulnerability occurs when an application accepts user input and fails to properly sanitize special characters that can trigger…

Recursos

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