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HTTP request smuggling

Need​

Consistent processing of HTTP requests by all entities involved

Context​

  • Usage of Go 1.16 for building high-performance and scalable applications
  • Usage of Gin for building web applications in Go
  • Usage of socket.io for real-time communication between the server and clients
  • Usage of net/http for building HTTP servers in a Node.js application

Description​

Non compliant code​

package main

import (
	"io"
	"net/http"
	"github.com/gin-gonic/gin"
)

func main() {
	r := gin.Default()
	r.POST("/process", func(c *gin.Context) {
		body := io.LimitReader(c.Request.Body, 1048576)
		c.Request.Body = http.MaxBytesReader(c.Writer, body, 1048576)

		// Process the request
		// ...
	})

	r.Run() // listen and serve on 0.0.0.0:8080
}

In the above code, the HTTP POST request to the /process endpoint is processed by the Gin web framework. The io.LimitReader function is used to limit the size of the request body to 1MB. The http.MaxBytesReader function is then used to further limit the size of the request body to 1MB.

This code is vulnerable to HTTP request smuggling because it uses two different methods to limit the size of the request body. The io.LimitReader function and the http.MaxBytesReader function may interpret the request body differently, especially if the request body is malformed.

For example, if the request body contains a Content-Length header with a value less than the actual size of the body, the io.LimitReader function will process the entire body, while the http.MaxBytesReader function will only process the body up to the Content-Length value. This discrepancy can be exploited by an attacker to smuggle a request past the http.MaxBytesReader function.

To fix this vulnerability, you should ensure that all entities that process HTTP requests in your application interpret the requests consistently. This can be achieved by using only one method to limit the size of the request body, or by validating the Content-Length header before processing the request body.

Steps​

  • Ensure that the web server software used by the entities involved in processing requests is consistent in delimiting requests.
  • Implement proper request validation and sanitization to prevent malformed requests from being processed.
  • Use a secure and up-to-date version of the web server software to minimize the risk of vulnerabilities.
  • Regularly update and patch the dependencies used by the application, including the gin framework, to address any known security issues.
  • Implement secure coding practices to prevent other common web vulnerabilities, such as cross-site scripting (XSS) and SQL injection.

Compliant code​

package main

import (
	"io"
	"net/http"
	"github.com/gin-gonic/gin"
)

func main() {
	r := gin.Default()
	r.Use(RequestSanitizer())
	r.POST("/process", func(c *gin.Context) {
		body := io.LimitReader(c.Request.Body, 1048576)
		c.Request.Body = http.MaxBytesReader(c.Writer, body, 1048576)

		// Process the request
		// ...
	})

	r.Run() // listen and serve on 0.0.0.0:8080
}

func RequestSanitizer() gin.HandlerFunc {
	return func(c *gin.Context) {
		// Implement request sanitization logic here
		// ...
		c.Next()
	}
}

The updated code includes a middleware function RequestSanitizer that is used to sanitize incoming HTTP requests. This function is added to the gin router with the Use function, which ensures that it is called for every request that the router handles.

The RequestSanitizer function is a placeholder for the actual sanitization logic. This logic should be designed to reject any malformed requests that could be used to exploit the HTTP request smuggling vulnerability. The exact implementation of this function will depend on the specific requirements of the application and the nature of the requests it needs to handle.

In addition to the RequestSanitizer middleware, it is also important to ensure that all entities involved in processing requests (such as proxies and firewalls) use consistent methods for delimiting requests. This can help to prevent inconsistencies that could be exploited to smuggle requests.

Finally, it is recommended to keep the gin framework and all other dependencies up-to-date to minimize the risk of other vulnerabilities. Regularly updating and patching these dependencies can help to address any known security issues.

References​

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