Snapshots for IPC Fuzzing – Mozilla Hacks – The Web Developer Blog

Process separation is one of the corners of the firefox security model. INTEAD OF Running Firefox as a Single Process, Multiple Process with Different Privileges Communicate with Each Other Via Inter-Prosess Communication (IPC). For example: loading a website, processing its resources, and rendering it is done by an islated Content process With a very restrictive sandbox, whereas critical operations such as file system access are only allowed to be executed in the Parent process,

By running potentially harmful code with lower privateages, the impact of a potential code execution vulnerability is mitigated. In order to Gain full control, the attacker now needs to find a second vulnerability that allows bypassing these privatege restrictions – which is colloquelly KNOWN as a “Sandbox Escape,

In order to achieve a sandbox escape, an attacker essentially has two options: the first one is to directly attached the unde which the underlying operating system from within the Compromised content. Since every process needs to interact with the operating system for various tasks, an attacker can focus on Finding Bugs in these interfaces to elevate privileges.

Since we have Alredy deployed Changes to Firefox that Severely Limit The OS Interfaces Exped to Low-Privilege Processes, The Second Attack Option BCOOMES More Interesting: Exploiting Bugs in Privileged IPC EndPoints. Since Low Privilege Content Processes Need to Interact with the Privileged Parent Process, The Parent Needs to Expaose Certain Interfaces.

If these interfaces do not perform the Necessary Security Checks or Contain Memory Safety Errors, The Content Process Might Be Able to Exclusive them and Perform Actions with Higherges, Possibly Leading to an Entre Parent Process takeover.

Traditionally, fuzzing has said multiple success stories in the history of mozilla and allowed us to find all sorts of problems of problems including security vulnerabilites in our code. However, applying fuzzing to our critical ipc interfaces Historically Always Been DifacityThis is primarily because IPC interfaces cannot be tested in isolation, IE require the full browser for testing, and becoming Incorrect Usage of IPC Interfaces CAN FORCE BROWSER RESTARS who Prohibitive Amount of Laigncy Between Iterations.

To find a solution to this challenge, we engaged with the research communication to apply a new method of Rewinding Application State During Fuzzing. We Saw our first results with this approach in 2021 using an experienced The Open Source Snapshot Fuzzing tool Called “Nyx”,

As of 2024, we are happy to announs that we are running various Snapshot fuzzing Targets for IPC in Production. Snapshot fuzzing is a new technology that has become more popular in recent years and we are proud of our role in bringing it from concept to practice.

Using this Technology we have alredy been able to identify and fix a number of potential problems In our IPC layer and we will continue to improve our testing to provide you with the most secure version of firfox.

If you’d like to know more, or even consider contributing to mozilla, check out Our post on the security blog Explaining the Technical Architecture Behind this new tool.