CWE-444 Base Incompleto

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

This weakness occurs when a proxy, firewall, or other intermediary HTTP agent interprets a malformed HTTP request or response differently than the final destination server or client. This…

Definición

What is CWE-444?

This weakness occurs when a proxy, firewall, or other intermediary HTTP agent interprets a malformed HTTP request or response differently than the final destination server or client. This inconsistency allows an attacker to craft messages that bypass the intermediary's security checks.
HTTP request smuggling exploits differences in how web servers, clients, and intermediary devices (like load balancers, reverse proxies, or WAFs) parse ambiguous HTTP messages. An attacker can inject conflicting headers—such as duplicate `Content-Length` or `Transfer-Encoding` fields—causing the intermediary and the backend server to see two different requests or responses in the same network stream. This lets malicious traffic slip through undetected. This vulnerability typically stems from using outdated HTTP parsing libraries or mismatched protocol versions between system components. To prevent it, developers must ensure all HTTP agents in the data flow use consistent, up-to-date parsing logic and rigorously validate message formatting.
Impacto en el mundo real

Real-world CVEs caused by CWE-444

  • CVE-2022-24766

    SSL/TLS-capable proxy allows HTTP smuggling when used in tandem with HTTP/1.0 services, due to inconsistent interpretation and input sanitization of HTTP messages within the body of another message

  • CVE-2021-37147

    Chain: caching proxy server has improper input validation (CWE-20) of headers, allowing HTTP response smuggling (CWE-444) using an "LF line ending"

  • CVE-2020-8287

    Node.js platform allows request smuggling via two Transfer-Encoding headers

  • CVE-2006-6276

    Web servers allow request smuggling via inconsistent HTTP headers.

  • CVE-2005-2088

    HTTP server allows request smuggling with both a "Transfer-Encoding: chunked" header and a Content-Length header

  • CVE-2005-2089

    HTTP server allows request smuggling with both a "Transfer-Encoding: chunked" header and a Content-Length header

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

  1. 1

    In the following example, a malformed HTTP request is sent to a website that includes a proxy server and a web server with the intent of poisoning the cache to associate one webpage with another malicious webpage.

  2. 2

    When this request is sent to the proxy server, the proxy server parses the first four lines of the POST request and encounters the two "Content-Length" headers. The proxy server ignores the first header, so it assumes the request has a body of length 54 bytes. Therefore, it treats the data in the next three lines that contain exactly 54 bytes as the first request's body:

  3. 3

    The proxy then parses the remaining bytes, which it treats as the client's second request:

  4. 4

    The original request is forwarded by the proxy server to the web server. Unlike the proxy, the web server uses the first "Content-Length" header and considers that the first POST request has no body.

  5. 5

    Because the web server has assumed the original POST request was length 0, it parses the second request that follows, i.e. for GET /poison.html:

Ejemplo de código vulnerable

Vulnerable code

In the following example, a malformed HTTP request is sent to a website that includes a proxy server and a web server with the intent of poisoning the cache to associate one webpage with another malicious webpage.

Vulnerable 
POST http://www.website.com/foobar.html HTTP/1.1
 Host: www.website.com
 Connection: Keep-Alive
 Content-Type: application/x-www-form-urlencoded
 Content-Length: 0
 Content-Length: 54

 GET /poison.html HTTP/1.1
 Host: www.website.com
 Bla: GET http://www.website.com/page_to_poison.html HTTP/1.1
 Host: www.website.com
 Connection: Keep-Alive
Payload del atacante

In the following example, a malformed HTTP request is sent to a website that includes a proxy server and a web server with the intent of poisoning the cache to associate one webpage with another malicious webpage.

Payload del atacante 
POST http://www.website.com/foobar.html HTTP/1.1
 Host: www.website.com
 Connection: Keep-Alive
 Content-Type: application/x-www-form-urlencoded
 Content-Length: 0
 Content-Length: 54

 GET /poison.html HTTP/1.1
 Host: www.website.com
 Bla: GET http://www.website.com/page_to_poison.html HTTP/1.1
 Host: www.website.com
 Connection: Keep-Alive
Ejemplo de código seguro

Secure Java

Additionally, if a web application includes a Java servlet for processing requests, the servlet can check for multiple "Content-Length" headers and if they are found the servlet can return an error response thereby preventing the poison page to be cached, as shown below.

Seguro Java 
protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
```
// Set up response writer object* 
  		...
  		try { 
  		```
```
// check for multiple content length headers* 
  				Enumeration contentLengthHeaders = request.getHeaders("Content-Length"); 
  				int count = 0; 
  				while (contentLengthHeaders.hasMoreElements()) { 
  				```
  					count++; 
  				} 
  				if (count > 1) { 
```
// output error response* } 
  				else { 
  				```
```
// process request* } 
  				} catch (Exception ex) {...}}
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-444

  • Implementation Use a web server that employs a strict HTTP parsing procedure, such as Apache [REF-433].
  • Implementation Use only SSL communication.
  • Implementation Terminate the client session after each request.
  • System Configuration Turn all pages to non-cacheable.
Señales de detección

How to detect CWE-444

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-444 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-444?

This weakness occurs when a proxy, firewall, or other intermediary HTTP agent interprets a malformed HTTP request or response differently than the final destination server or client. This inconsistency allows an attacker to craft messages that bypass the intermediary's security checks.

¿Qué gravedad tiene CWE-444?

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-444?

MITRE lists the following affected platforms: Web Based.

¿Cómo puedo prevenir CWE-444?

Use a web server that employs a strict HTTP parsing procedure, such as Apache [REF-433]. Use only SSL communication.

¿Cómo detecta y corrige Plexicus CWE-444?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-444 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-444?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/444.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-444

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Recursos

Further reading

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