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CWE-289 Base Incompleto
Authentication Bypass by Alternate Name
This vulnerability occurs when a system checks access based on a resource or user name, but fails to account for all the different names or aliases that could refer to the same entity, allowing…
Definição
What is CWE-289?
This vulnerability occurs when a system checks access based on a resource or user name, but fails to account for all the different names or aliases that could refer to the same entity, allowing attackers to bypass authentication.
This flaw often appears in systems that rely on simple string matching for access control. For example, a file server might block access to 'admin.txt' but overlook 'ADMIN.TXT', 'Admin.Txt', or a symlink pointing to the same file. Similarly, a user authentication system might verify 'administrator' but not check for 'admin', 'root', or other common aliases for privileged accounts. Attackers exploit this by simply using an alternate name the system doesn't recognize as restricted.
To prevent this, developers must implement canonicalization, where all names are resolved to a single, standard form before the security check. This means normalizing file paths, converting usernames to a consistent case, and resolving symbolic links. Access control logic should never rely on raw, unvalidated input strings. Instead, it should compare the canonical identity of the resource or user against a policy that is enforced consistently for all access attempts.
Impacto no mundo real
Real-world CVEs caused by CWE-289
-
Protection mechanism that restricts URL access can be bypassed using URL encoding.
-
Bypass of authentication for files using "\" (backslash) or "%5C" (encoded backslash).
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-289
- Architecture and Design Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
- Implementation Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Implementation Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Sinais de deteção
How to detect CWE-289
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-289
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-289?
Qual a gravidade do CWE-289?
Que linguagens ou plataformas são afetadas pelo CWE-289?
Como posso prevenir o CWE-289?
Como é que o Plexicus deteta e corrige o CWE-289?
Onde posso saber mais sobre o CWE-289?
Frequently asked questions
O que é o CWE-289?
This vulnerability occurs when a system checks access based on a resource or user name, but fails to account for all the different names or aliases that could refer to the same entity, allowing attackers to bypass authentication.
Qual a gravidade do CWE-289?
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-289?
A MITRE não especificou as plataformas afetadas por este CWE — pode aplicar-se à maioria das stacks de aplicações.
Como posso prevenir o CWE-289?
Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names. Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the…
Como é que o Plexicus deteta e corrige o CWE-289?
O motor SAST do Plexicus correlaciona a assinatura de fluxo de dados do CWE-289 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-289?
A MITRE publica a definição canónica em https://cwe.mitre.org/data/definitions/289.html. Pode também consultar a documentação da OWASP e do NIST para orientações adjacentes.
Fraquezas relacionadas
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