CWE-1286 Base Incompleto

Improper Validation of Syntactic Correctness of Input

This vulnerability occurs when software expects input in a specific, well-structured format but fails to properly check that the incoming data actually follows those rules.

Definición

What is CWE-1286?

This vulnerability occurs when software expects input in a specific, well-structured format but fails to properly check that the incoming data actually follows those rules.
Modern applications often rely on structured data formats like JSON, XML, YAML, or even code snippets. These formats have strict grammatical rules (syntax) that parsers use to understand the data. When you don't validate that untrusted input correctly adheres to this expected syntax, you hand control of your parser to an attacker. They can send malformed data designed to crash the parser, trigger obscure error messages that leak system information, or exploit hidden bugs in the parsing logic itself. Robust input validation is your first line of defense. Instead of assuming data is well-formed, actively verify its syntactic correctness before any processing begins. Use established, security-hardened parsers with strict mode enabled and define a precise schema for all expected inputs. This practice prevents attackers from manipulating the parsing stage to cause denial-of-service, information disclosure, or create an opening for more severe injection attacks.
Impacto en el mundo real

Real-world CVEs caused by CWE-1286

  • CVE-2016-4029

    Chain: incorrect validation of intended decimal-based IP address format (CWE-1286) enables parsing of octal or hexadecimal formats (CWE-1389), allowing bypass of an SSRF protection mechanism (CWE-918).

  • CVE-2007-5893

    HTTP request with missing protocol version number leads to crash

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

  1. 1

    Identifica una ruta de código que maneje entrada no confiable sin validación.

  2. 2

    Crea un payload que ejercite el comportamiento inseguro — inyección, traversal, overflow o abuso de lógica.

  3. 3

    Envía el payload a través de una solicitud normal y observa la reacción de la aplicación.

  4. 4

    Itera hasta que la respuesta filtre datos, ejecute código del atacante o escale privilegios.

Ejemplo de código vulnerable

Vulnerable Java

The following code loads and parses an XML file.

Vulnerable Java 
```
// Read DOM* 
  try {
  ```
  	...
  	DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
  	factory.setValidating( false );
  	....
  	c_dom = factory.newDocumentBuilder().parse( xmlFile );
  } catch(Exception ex) {
  	...
  }
Ejemplo 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 prevención

How to prevent CWE-1286

  • 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.
Señales de detección

How to detect CWE-1286

SAST High

Ejecuta análisis estático (SAST) sobre el código buscando el patrón inseguro en el flujo de datos.

DAST Moderate

Ejecuta pruebas dinámicas de seguridad de aplicaciones (DAST) contra el endpoint en vivo.

Runtime Moderate

Vigila los logs en tiempo de ejecución para detectar trazas de excepción inusuales, entradas malformadas o intentos de bypass de autorización.

Code review Moderate

Revisión de código: marca cualquier código nuevo que maneje entrada desde esta superficie sin usar los helpers validados del framework.

Auto-corrección de Plexicus

Plexicus detecta automáticamente CWE-1286 y abre un PR de corrección en menos de 60 segundos.

Codex Remedium escanea cada commit, identifica esta debilidad concreta y entrega un pull request listo para revisión con el parche. Sin tickets. Sin traspasos.

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Preguntas frecuentes

Frequently asked questions

¿Qué es CWE-1286?

This vulnerability occurs when software expects input in a specific, well-structured format but fails to properly check that the incoming data actually follows those rules.

¿Qué gravedad tiene CWE-1286?

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-1286?

MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.

¿Cómo puedo prevenir CWE-1286?

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…

¿Cómo detecta y corrige Plexicus CWE-1286?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-1286 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-1286?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/1286.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-1286

CWE-20 Padre

Improper Input Validation

This vulnerability occurs when an application accepts data from an external source but fails to properly verify that the data is safe and…

CWE-102 Hermano

Struts: Duplicate Validation Forms

This vulnerability occurs when an application defines multiple Struts validation forms with identical names. The framework then…

CWE-103 Hermano

Struts: Incomplete validate() Method Definition

This vulnerability occurs in a Struts application when a validator form either completely omits a validate() method or includes one but…

CWE-104 Hermano

Struts: Form Bean Does Not Extend Validation Class

This vulnerability occurs in Apache Struts applications when a form bean class does not properly extend the framework's validation class.…

CWE-105 Hermano

Struts: Form Field Without Validator

This vulnerability occurs when a Struts application form contains an input field that lacks a corresponding validator, leaving it open to…

CWE-106 Hermano

Struts: Plug-in Framework not in Use

This weakness occurs when a Java application, particularly one using the Struts framework, does not implement a structured input…

CWE-107 Hermano

Struts: Unused Validation Form

This vulnerability occurs when a Struts application contains validation form definitions that are no longer linked to any active form or…

CWE-108 Hermano

Struts: Unvalidated Action Form

In Apache Struts, every Action Form that processes user input must have a corresponding validation form configured. Missing this…

CWE-109 Hermano

Struts: Validator Turned Off

This vulnerability occurs when an application built with Apache Struts intentionally disables its built-in validation framework. By…

Recursos

Further reading

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