CWE-201 Base Borrador

Insertion of Sensitive Information Into Sent Data

This vulnerability occurs when an application sends data to an external party, but accidentally includes sensitive information—like passwords, keys, or personal data—that the recipient should not be…

Definición

What is CWE-201?

This vulnerability occurs when an application sends data to an external party, but accidentally includes sensitive information—like passwords, keys, or personal data—that the recipient should not be able to access.
This flaw often happens because of overly broad data selection or logging mechanisms that package more information than necessary for a given transaction. For example, an API response might return an entire user object, including internal fields like hashed passwords or security questions, instead of just the needed profile data. Developers should carefully review all data payloads sent to clients, third-party services, or logs, ensuring they follow the principle of least privilege and expose only what is explicitly required. Catching these leaks manually is challenging, as sensitive data can be buried deep in nested objects or only appear under specific conditions. While SAST tools can flag patterns of data exposure, Plexicus uses AI to analyze data flows in context and suggest precise code fixes—such as implementing stricter output filters or using data sanitization libraries—saving hours of manual review and reducing the risk of accidental disclosure across your entire application stack.
Vulnerability Diagram CWE-201
Sensitive Data in Sent Data Client GET /me API response "name": "alice", "email": "a@x.com", "ssn": "123-45-6789", "hash": "$2b$…", "internalId": 42, "isAdmin": true # UI only uses name+email Client devtools read full JSON API returns more fields than the UI uses; extras are visible to the client.
Impacto en el mundo real

Real-world CVEs caused by CWE-201

  • CVE-2022-0708

    Collaboration platform does not clear team emails in a response, allowing leak of email addresses

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 SQL

The following is an actual MySQL error statement:

Vulnerable SQL 
Warning: mysql_pconnect(): Access denied for user: 'root@localhost' (Using password: N1nj4) in /usr/local/www/wi-data/includes/database.inc on line 4
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-201

  • Requirements Specify which data in the software should be regarded as sensitive. Consider which types of users should have access to which types of data.
  • Implementation Ensure that any possibly sensitive data specified in the requirements is verified with designers to ensure that it is either a calculated risk or mitigated elsewhere. Any information that is not necessary to the functionality should be removed in order to lower both the overhead and the possibility of security sensitive data being sent.
  • System Configuration Setup default error messages so that unexpected errors do not disclose sensitive information.
  • Architecture and Design Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area. Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
Señales de detección

How to detect CWE-201

Automated Static Analysis High

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Auto-corrección de Plexicus

Plexicus detecta automáticamente CWE-201 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-201?

This vulnerability occurs when an application sends data to an external party, but accidentally includes sensitive information—like passwords, keys, or personal data—that the recipient should not be able to access.

¿Qué gravedad tiene CWE-201?

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-201?

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

¿Cómo puedo prevenir CWE-201?

Specify which data in the software should be regarded as sensitive. Consider which types of users should have access to which types of data. Ensure that any possibly sensitive data specified in the requirements is verified with designers to ensure that it is either a calculated risk or mitigated elsewhere. Any information that is not necessary to the functionality should be removed in order to lower both the overhead and the possibility of security sensitive data being sent.

¿Cómo detecta y corrige Plexicus CWE-201?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-201 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-201?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/201.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-201

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CWE-1295 Hermano

Debug Messages Revealing Unnecessary Information

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CWE-1431 Hermano

Driving Intermediate Cryptographic State/Results to Hardware Module Outputs

This vulnerability occurs when a hardware cryptographic module leaks sensitive internal data through its output channels. Instead of only…

CWE-203 Hermano

Observable Discrepancy

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CWE-209 Hermano

Generation of Error Message Containing Sensitive Information

This vulnerability occurs when an application reveals sensitive details about its internal systems, user data, or environment within error…

CWE-213 Hermano

Exposure of Sensitive Information Due to Incompatible Policies

This vulnerability occurs when a system's data handling aligns with the developer's security rules but accidentally reveals information…

CWE-215 Hermano

Insertion of Sensitive Information Into Debugging Code

This vulnerability occurs when developers embed sensitive data, such as passwords or API keys, within debugging statements like logs or…

Recursos

Further reading

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