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CWE-180 Variante Borrador
Incorrect Behavior Order: Validate Before Canonicalize
This vulnerability occurs when a system checks user input for malicious content before standardizing its format, allowing specially crafted data to bypass security checks.
Definición
What is CWE-180?
This vulnerability occurs when a system checks user input for malicious content before standardizing its format, allowing specially crafted data to bypass security checks.
When validation runs before canonicalization (the process of converting data into a standard, consistent form), attackers can exploit the gap between these two steps. They can submit input that appears safe during the initial check but transforms into a dangerous payload after it's standardized. For example, an attacker might use alternate character encodings, multiple slashes, or dot sequences that resolve to a forbidden path after canonicalization.
This flaw effectively neutralizes security defenses like allow-lists or injection filters, creating a false sense of security. To prevent this, always canonicalize input first—convert it to its simplest, canonical form—and then perform validation and sanitization on that standardized data. This ensures your security logic evaluates the actual data the application will use.
Impacto en el mundo real
Real-world CVEs caused by CWE-180
-
Product allows remote attackers to view restricted files via an HTTP request containing a "*" (wildcard or asterisk) character.
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Product modifies the first two letters of a filename extension after performing a security check, which allows remote attackers to bypass authentication via a filename with a .ats extension instead of a .hts extension.
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Database consumes an extra character when processing a character that cannot be converted, which could remove an escape character from the query and make the application subject to SQL injection attacks.
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Overlaps "fakechild/../realchild"
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Product checks URI for "<" and other literal characters, but does it before hex decoding the URI, so "%3E" and other sequences are allowed.
Cómo lo explotan los atacantes
Ruta del atacante paso a paso
- 1
The following code attempts to validate a given input path by checking it against an allowlist and then return the canonical path. In this specific case, the path is considered valid if it starts with the string "/safe_dir/".
- 2
The problem with the above code is that the validation step occurs before canonicalization occurs. An attacker could provide an input path of "/safe_dir/../" that would pass the validation step. However, the canonicalization process sees the double dot as a traversal to the parent directory and hence when canonicized the path would become just "/".
- 3
To avoid this problem, validation should occur after canonicalization takes place. In this case canonicalization occurs during the initialization of the File object. The code below fixes the issue.
Ejemplo de código vulnerable
Vulnerable Java
The following code attempts to validate a given input path by checking it against an allowlist and then return the canonical path. In this specific case, the path is considered valid if it starts with the string "/safe_dir/".
String path = getInputPath();
if (path.startsWith("/safe_dir/"))
{
File f = new File(path);
return f.getCanonicalPath();
} Ejemplo de código seguro
Secure Java
To avoid this problem, validation should occur after canonicalization takes place. In this case canonicalization occurs during the initialization of the File object. The code below fixes the issue.
String path = getInputPath();
File f = new File(path);
if (f.getCanonicalPath().startsWith("/safe_dir/"))
{
return f.getCanonicalPath();
} 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-180
- 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.
Señales de detección
How to detect CWE-180
Ejecuta pruebas dinámicas de seguridad de aplicaciones (DAST) contra el endpoint en vivo.
Vigila los logs en tiempo de ejecución para detectar trazas de excepción inusuales, entradas malformadas o intentos de bypass de autorización.
Revisión de código: marca cualquier código nuevo que maneje entrada desde esta superficie sin usar los helpers validados del framework.
CWE-180
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.
Preguntas frecuentes ¿Qué es CWE-180?
¿Qué gravedad tiene CWE-180?
¿Qué lenguajes o plataformas se ven afectados por CWE-180?
¿Cómo puedo prevenir CWE-180?
¿Cómo detecta y corrige Plexicus CWE-180?
¿Dónde puedo aprender más sobre CWE-180?
Frequently asked questions
¿Qué es CWE-180?
This vulnerability occurs when a system checks user input for malicious content before standardizing its format, allowing specially crafted data to bypass security checks.
¿Qué gravedad tiene CWE-180?
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-180?
MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.
¿Cómo puedo prevenir CWE-180?
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.
¿Cómo detecta y corrige Plexicus CWE-180?
El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-180 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-180?
MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/180.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.
Debilidades relacionadas
Weaknesses related to CWE-180
CWE-179 Padre
Incorrect Behavior Order: Early Validation
This vulnerability occurs when an application validates user input before applying security filters or data normalization. Attackers can…
CWE-181 Hermano
Incorrect Behavior Order: Validate Before Filter
This vulnerability occurs when a system checks user input for validity before cleaning or filtering it. This flawed sequence allows…
¿Listo para validar lo que importa?
Listo para validar lo que importa.
Plexicus es Proof-Driven AppSec: hallazgos validados, comprensión contextual y remediación revisada — anclada en evidencia, acotada contigo.