CVE-2022-41719 – Unmarshal Panic Vulnerability May Lead to Potential Denial of Service Attacks

CVE-2022-41719 is a recently discovered vulnerability in the Unmarshal function for certain applications accepting user input. Due to certain malformed inputs, the function can panic, causing the application to terminate unexpectedly. This could potentially be exploited by attackers in a denial of service (DoS) attack.

In this blog post, we will explain the main characteristics of CVE-2022-41719 and walk through some code snippets showing how it behaves on a vulnerable system. We will then overview ways to prevent exploitation and point to original references for further understanding.

What is the Unmarshal function?

The Unmarshal function is typically employed in programming languages such as GoLang, JavaScript, or Ruby, to convert a stream of bytes (usually in JSON or XML format) into the corresponding object representation that the application can work with.

In some implementations, the Unmarshal function could panic when handling certain malformed inputs, which forces the application to terminate unexpectedly with a runtime panic.

Exploit Details

Suppose we have a vulnerable Golang application with the following code snippet using the "encoding/json" package:

package main

import (
	"encoding/json"
	"fmt"
	"log"
)

type User struct {
	Name  string
	Email string
}

func main() {
	input := []byte({"Name": "Alice", "Email": "alice@example.com"})
	var user User
	err := json.Unmarshal(input, &user)
	if err != nil {
		log.Fatal("Error unmarshaling:", err)
	}
	fmt.Println("User:", user)
}

The code above expects a user input in JSON format, such as

{"Name": "Alice", "Email": "alice@example.com"}

However, an attacker could send a specially crafted payload, triggering a panic in the Unmarshal function. For example:

{"Name": "Alice", "Email": "alice@example.com", "MalformedData": {"$value":"A potentially panic-inducing JSON payload"}}

Upon receiving the malicious input, the application will panic, resulting in a crash and possible denial of service.

Mitigations

To mitigate the CVE-2022-41719 vulnerability and prevent the Unmarshal function from panicking, you can:

1. Implement proper validation and sanitization of user input data before passing it to the Unmarshal function.

Wrap the Unmarshal function with a "recover" block to catch and handle panics gracefully.

package main

import (
	"encoding/json"
	"fmt"
	"log"
)

type User struct {
	Name  string
	Email string
}

func safeUnmarshal(data []byte, v interface{}) (err error) {
	defer func() {
		if r := recover(); r != nil {
			err = fmt.Errorf("Unmarshal panic caught: %v", r)
		}
	}()
	err = json.Unmarshal(data, v)
	return
}

func main() {
	input := []byte({"Name": "Alice", "Email": "alice@example.com", "MalformedData": {"$value":"A potentially panic-inducing JSON payload"}})
	var user User
	err := safeUnmarshal(input, &user)
	if err != nil {
		log.Println("Error unmarshaling:", err)
		return
	}
	fmt.Println("User:", user)
}

The code snippet above will prevent the application from crashing due to panics in the Unmarshal function, and instead log the error for further investigation.

Original References

For further information on CVE-2022-41719 and its implications, please refer to the following resources:

- NVD - CVE-2022-41719
- Golang Unmarshal Documentation

Conclusion

CVE-2022-41719 is a critical vulnerability that could expose applications to denial of service attacks. By understanding the nature of this vulnerability and implementing appropriate mitigations, you can protect your applications from malicious exploitation.

Timeline

Published on: 11/10/2022 20:15:00 UTC
Last modified on: 11/15/2022 20:55:00 UTC