In this long read post, we will discuss the recently discovered memory safety bugs in Firefox 133 and Thunderbird 133, which have been assigned the CVE number CVE-2025-0247. These vulnerabilities have been shown to cause memory corruption and, with enough effort, can potentially be exploited to run arbitrary code. As such, it is crucial for users to update to the latest version of Firefox (134) and Thunderbird (134) to avoid falling victim to these security threats.

Background

Memory safety is a critical aspect of modern software development, as it ensures that a program operates correctly and does not inadvertently access or modify memory in an unauthorized manner. Despite the importance of this concept, software developers occasionally introduce memory safety bugs in their applications, opening up the potential for attackers to exploit these vulnerabilities to gain unauthorized access to systems or execute malicious code.

Recently, security researchers discovered several memory safety bugs in Firefox 133 and Thunderbird 133. Upon further investigation, some of these bugs demonstrated evidence of memory corruption, thereby increasing the possibility that attackers could develop exploits to run arbitrary code.

Original References

CVE-2025-0247 on the Mitre CVE database:
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-0247

Mozilla Foundation Security Advisory:
https://www.mozilla.org/en-US/security/advisories/mfsa2025-24/

The Vulnerabilities

CVE-2025-0247 primarily affects Firefox versions < 134 and Thunderbird versions < 134. This collection of memory safety bugs has a wide-ranging impact and could be exploited by an attacker in various ways. Some of these vulnerabilities involve issues with memory allocation, deallocation, or access control, while others pertain to the improper handling of pointers, leading to memory corruption.

One example of a memory safety bug in Firefox 133 and Thunderbird 133 is as follows

void vulnerable_function(char* input) {
    char buffer[256];
    strcpy(buffer, input);
}

In this code snippet, the vulnerable_function takes input from a user and copies it into a buffer. However, the function does not properly validate the input, leading to the risk of a buffer overflow attack. An attacker could exploit this vulnerability by supplying a carefully crafted input string that overwrites adjacent memory, causing memory corruption and potentially executing arbitrary code.

Exploit Details

To develop a successful exploit for CVE-2025-0247, an attacker would need to invest significant effort in understanding the affected software's underlying memory management mechanisms, as well as identifying suitable access points to trigger the memory safety bugs. These exploits would likely involve crafting malicious inputs that, when processed by the vulnerable software, result in memory corruption and ultimately arbitrary code execution.

Mitigation

Users of Firefox and Thunderbird should immediately update their software to the latest version, as Mozilla has released patches for these vulnerabilities in Firefox 134 and Thunderbird 134.

Firefox Update

https://www.mozilla.org/en-US/firefox/new/

Thunderbird Update

https://www.thunderbird.net/en-US/

Conclusion

Memory safety bugs, such as those present in Firefox 133 and Thunderbird 133 (CVE-2025-0247), pose significant risks to users, as they can potentially be exploited to run arbitrary code and jeopardize system security. It is essential for users to stay up-to-date with software updates and security advisories to ensure the protection of their systems and mitigate the risk of exploitation.

Timeline

Published on: 01/07/2025 16:15:39 UTC
Last modified on: 01/14/2025 17:15:20 UTC