Hey folks! Today, we're going to delve into a security vulnerability, specifically identified as CVE-2024-3859. This vulnerability affects 32-bit versions of Firefox (prior to version 125), Firefox ESR (prior to version 115.10), and Thunderbird (prior to version 115.10). It is an integer-overflow vulnerability that can potentially be exploited through a specially crafted OpenType font, leading to an out-of-bounds read scenario.

Let's take a step-by-step look at what this vulnerability is, how it works, and what can be done to mitigate its impact.

Understanding the Vulnerability

An integer-overflow is a type of vulnerability that occurs when an arithmetic operation results in a value that is too large to be stored in the allocated memory space. In this case, the vulnerability can be exploited by an attacker using a malicious OpenType font file. OpenType is a popular font format used in various operating systems and applications, including Firefox and Thunderbird.

The integer-overflow vulnerability in these Mozilla applications can lead to an out-of-bounds read, which in turn may have other potentially dangerous consequences, such as information disclosure or even remote code execution.

Exploit Details

In order to exploit this vulnerability, an attacker would first need to create a malicious OpenType font file containing specific data that triggers the integer-overflow condition. The following code snippet shows an example of such a font file:

// Malicious OpenType font file (simplified)
...
const OTF_TABLE_ENTRY OpenTypeOffsetTable[] = {
  {OTF_TAG('c', 'm', 'a', 'p'), x10000}, // cmap table (start at x10000)
};
...
const OTF_SUB_HEADER subHeader = {
  xFFFF, // format (forces an integer overflow)
  x000, // length
  x000, // language
};
...

This malformed OpenType font file can be embedded into a webpage or an email, which when rendered by the vulnerable versions of Firefox or Thunderbird, could result in an out-of-bounds read, as shown in the following sample code:

// Pseudo-code for reading font data:
void readFontData(const OTF_TABLE_ENTRY* tableEntry) {
  uint32_t start = tableEntry->offset;
  uint32_t format = read16(start);
  uint32_t length = read16(start + 2);
  uint32_t totalSize = format + length; // Integer overflow occurs here

  // Read the font data starting at start + totalSize,
  // leading to an out-of-bounds read
  for (uint32_t i = ; i < totalSize; i++) {
    readByte(start + totalSize + i); 
  }
}

As we can see, the presence of a malicious OpenType font file in the vulnerable application environment can lead to unintended memory access, thereby posing a security risk.

Original References

For those interested in further information on this vulnerability, you can refer to the following resources:

1. CVE-2024-3859 - MITRE
2. Mozilla Foundation Security Advisory - MFSA-2025-26
3. Mozilla Security Bug 1578263

Mitigation

Fortunately, the good folks at Mozilla have already addressed this vulnerability in their latest software releases. To protect yourself from potential exploits, make sure to update your Firefox, Firefox ESR, or Thunderbird to the following minimum versions:

Thunderbird 115.10

Always remember to keep your software up to date, and stay safe!

Conclusion

We hope that this article has given you a thorough understanding of the CVE-2024-3859 vulnerability affecting 32-bit Firefox, Firefox ESR, and Thunderbird applications. Integer-overflow vulnerabilities, like this one, can lead to serious consequences if left unaddressed. By staying informed and keeping our software updated, we can better protect ourselves and our systems from potential security risks.

As always, thanks for joining us on this deep dive into cybersecurity! If you have any thoughts or questions, feel free to leave them in the comments below. Until next time, stay secure!

Timeline

Published on: 04/16/2024 16:15:08 UTC
Last modified on: 07/03/2024 02:06:47 UTC