CVE-2023-25737: Firefox, Thunderbird, and Firefox ESR Vulnerability - Invalid Downcast in `nsTextNode` to `SVGElement`

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Introduction

Hello everyone! Today, we will discuss an important vulnerability that was discovered in the popular web browser Firefox, as well as its mail client Thunderbird and its extended support release (ESR) version. The vulnerability, assigned with the CVE identifier CVE-2023-25737, is concerning an invalid downcast from nsTextNode to SVGElement. In simpler terms, an object of one type, nsTextNode, was wrongly treated as an object of another type, SVGElement, which could lead to unexpected behavior.

Affected versions of the software include Firefox versions prior to 110, Thunderbird versions prior to 102.8, and Firefox ESR versions prior to 102.8.

This long read will explore the details of the discovered vulnerability, provide code snippets to showcase the threat, and provide you with helpful resources, including links to original references.

Background

The CVE-2023-25737 vulnerability is a result of an invalid downcast from the nsTextNode object to the SVGElement object. In object-oriented programming, casting is a way to convert an object of one type into another. A downcast is when you convert a base class object to a derived class object. In this case, the nsTextNode is mistakenly treated as if it were an object of type SVGElement, which leads to undefined behavior.

To better understand this vulnerability, let's look at a code snippet that demonstrates the issue

/* Incorrect downcast from nsTextNode to SVGElement */

// Create an instance of nsTextNode
RefPtr<nsTextNode> textNode = new nsTextNode();

// At some point in the code, textNode is cast to SVGElement
SVGElement* svgElement = static_cast<SVGElement*>(textNode.get());

// Now, a method from SVGElement is called on the textNode, leading to undefined behavior
svgElement->SomeSVGMethod();

In the code snippet above, we first create an instance of nsTextNode, and later in the code, we use a static_cast to "convert" the nsTextNode instance to an SVGElement. This is an invalid downcast, as nsTextNode is not derived from SVGElement. Calling a method of the SVGElement class on the incorrectly casted object will lead to undefined behavior, meaning that the outcome is unpredictable and can potentially be exploited by attackers.

Resolution

The developers working on Firefox, Thunderbird, and Firefox ESR have addressed this vulnerability by properly type-checking objects before attempting a downcast. Users of the affected software are encouraged to update their respective applications to the latest version to protect themselves against this vulnerability:

You can find the latest releases for the respective applications here

- Firefox
- Thunderbird
- Firefox ESR

For more information on this vulnerability, you can consult the following references

- Mozilla Security Advisory
- CVE-2023-25737 Details

Conclusion

This long read has given you an overview of the CVE-2023-25737 vulnerability, which affects Firefox, Thunderbird, and Firefox ESR. Understanding the details of vulnerabilities such as these is crucial in order to protect your software and stay secure online. Don't forget to update your applications to their latest version to safeguard yourself against potential attacks exploiting this vulnerability.

Timeline

Published on: 06/02/2023 17:15:00 UTC
Last modified on: 06/08/2023 16:09:00 UTC