The Mozilla Foundation recently disclosed multiple memory safety bugs, collectively known as CVE-2022-0511, affecting Firefox 96. These issues were identified and reported by Mozilla developers and community members, including Gabriele Svelto, Sebastian Hengst, Randell Jesup, Luan Herrera, Lars T. Hansen, and the Mozilla Fuzzing Team. In this long-read post, we will dive deep into some of the critical aspects of these bugs, explore possible code snippets, and provide links to original references.

While Mozilla was quick to address them, some of these memory safety bugs showed evidence of memory corruption, and it is presumed that, with enough effort, some could have been exploited to run arbitrary code. The vulnerability affects Firefox versions below 97.

Exploit Details

Memory safety bugs in software like Firefox can lead to severe security issues such as arbitrary code execution, denial of service, and unauthorized data access. In the case of CVE-2022-0511, the following memory corruption issues were reported:

Out-of-bounds memory reads and writes

The memory safety issues were initially discovered using various fuzz-testing tools employed by Mozilla's Fuzzing Team. Fuzzing is an automated testing method that involves providing malformed or unexpected inputs to a program with the goal of identifying vulnerabilities.

Here's a basic example of a UAF problem in C++

#include <iostream>

int main() {
    int *ptr = new int(42);

    delete ptr;

    std::cout << *ptr << std::endl; // Accessing freed memory

    return ;

This basic example demonstrates a UAF vulnerability, where *ptr is used after being freed, potentially leading to memory corruption.

A simple example of a data race issue in a multi-threaded Python program

import threading

counter = 

def thread_function():
    global counter
    for _ in range(10000):
        counter += 1

threads = []

for _ in range(10):
    t = threading.Thread(target=thread_function)

for t in threads:

print("Counter value:", counter)

The global variable 'counter' is shared by multiple threads and being updated without any synchronization mechanism, causing a data race condition.

An example of an out-of-bounds memory access issue in C

#include <stdio.h>

int main() {
  int array[5] = {1, 2, 3, 4, 5};

  for (int i = ; i <= 5; i++) {
    printf("%d\n", array[i]); // Out-of-bounds access at i == 5

  return ;

This example demonstrates an out-of-bounds memory access vulnerability in a simple array, which may lead to memory corruption issues.

Original References and Further Reading

The interested reader can learn more about these memory safety bugs and follow their progress through the following official resources:

1. Mozilla Foundation Security Advisory 2022-04
2. Common Vulnerabilities and Exposures-2022-0511
3. National Vulnerability Database-CVE-2022-0511

It is noteworthy that the latest version of Firefox, i.e., version 97, is not affected by these memory safety bugs. Users are strongly encouraged to upgrade to Firefox 97, ensuring a safer browsing experience.


Published on: 12/22/2022 20:15:00 UTC
Last modified on: 12/29/2022 18:53:00 UTC