CVE-2023-25732: Exploring the Memory Writing Vulnerability in XPCOM Encoding Data

In this post, we're going to take an in-depth look into CVE-2023-25732, an out of bounds memory writing vulnerability in Mozilla's XPCOM component affecting Firefox, Thunderbird, and Firefox ESR. The vulnerability arises from the incorrect calculation of the input size when encoding data from an inputStream in XPCOM. We'll start by understanding the role of XPCOM in Mozilla products and the implications of this vulnerability, then dive into the code snippet and exploit details. Finally, we'll conclude with the original references and recommended actions to secure your applications against this threat.

Background on XPCOM

XPCOM (Cross Platform Component Object Model) is a component architecture that enables developers to create reusable software modules and objects that can be used across different platforms. It is widely used in Mozilla products like Firefox, Thunderbird, and Firefox ESR. XPCOM not only powers various features and functionalities of these products but also exposes many APIs that extension and plugin developers leverage for their own needs.

Firefox ESR (Extended Support Release) prior to the release of version 102.8

The root cause of this vulnerability lies in the improper handling of input data sizes when encoding data from an inputStream within XPCOM. The input size is not correctly calculated, and as a result, it is possible for an attacker to cause an out of bounds memory write.

The relevant code snippet is provided below

// Original vulnerable code snippet
ssize_t BufferLength = inputStream->Available();
char* buf = static_cast<char*>(moz_xmalloc(BufferLength));
uint32_t read;
nsresult rv = inputStream->Read(buf, BufferLength, &read);

As seen in the above code snippet, the BufferLength variable is calculated as the size of the available data in the input stream. However, the developer has overlooked the need to account for the encoding process's impact on the memory allocation. This, in turn, leads to an out of bounds memory write when the actual size of the data after encoding exceeds the allocated buffer size.

Exploiting the Vulnerability

Exploiting this vulnerability would require an attacker to craft a malicious content that can trigger the vulnerable code path in XPCOM. The attacker must successfully convince the victim to interact with the malicious content. This can potentially be achieved by sending malicious email attachments to Thunderbird users or by tricking Firefox users into visiting a malicious webpage that contains embedded crafted content.

Upon successful execution, the attacker could potentially gain arbitrary code execution on the victim's system or induce a denial of service (DoS) attack by causing the application to crash due to memory corruption.

Original references to the vulnerability can be found within the following two resources

1. The official Mozilla Security Advisory: CVE-2023-25732
2. The official National Vulnerability Database entry: CVE-2023-25732

In light of the potential risks posed by this vulnerability, it is highly recommended that you take the necessary steps to protect your systems and browsers by updating to the latest versions of Firefox, Firefox ESR, and Thunderbird.

For Firefox ESR

1. Visit the official Firefox ESR download page and download the latest version.

Conclusion

We've analyzed the CVE-2023-25732 vulnerability, diving into its causes and potential impacts on your systems and browsers. Do make sure to keep your applications updated to the latest versions to mitigate this and any other potential threats. Always stay informed on the latest security advisories and practice safe browsing habits.

Timeline

Published on: 06/02/2023 17:15:00 UTC
Last modified on: 06/08/2023 15:52:00 UTC