Summary:  
A set of memory safety issues were found in Firefox 116, Firefox ESR 102.14 and 115.1, as well as Thunderbird 102.14 and 115.1. These bugs have potential for memory corruption, opening the door for attackers to possibly run arbitrary code. This article covers what these vulnerabilities mean, how they could be exploited, code examples, and where to find more information.

What Is CVE-2023-4584?

CVE-2023-4584 is a security vulnerability affecting Mozilla Firefox and Thunderbird from specific versions and earlier:

Thunderbird below 102.15 and 115.2

Overview from Mozilla:  
> Memory safety bugs present in Firefox 116, Firefox ESR 102.14, Firefox ESR 115.1, Thunderbird 102.14, and Thunderbird 115.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort, some of these could have been exploited to run arbitrary code.

Reference:  
- Mozilla Security Advisory 2023-29
- NVD - CVE-2023-4584

What Are Memory Safety Bugs?

Memory safety issues are programming bugs that allow a program to accidentally access or change memory it shouldn’t. This can cause crashes, data leaks, or (worse) allow attackers to run their own code.

Dangling Pointers: Pointers referencing deallocated memory.

Many critical browser vulnerabilities come from these bugs because browsers process content from all over the internet.

How Could CVE-2023-4584 Be Exploited?

Attackers exploit memory corruption in browsers by making the browser process unusual web content (malformed images, scripts, etc). If successful, they might execute malicious code on your machine, leading to data theft, ransomware, or further compromise.

Code Snippet: Illustrative Vulnerable Pattern

The exact details for CVE-2023-4584 haven’t been released publicly (for safety), but here's a simple C++ buffer overflow example, similar to bugs found in browsers:

#include <cstring>
#include <iostream>

void unsafe_copy(const char* user_input) {
    char buffer[64];
    strcpy(buffer, user_input); // No length check!
    std::cout << "Copied: " << buffer << std::endl;
}

int main(int argc, char** argv) {
    if(argc < 2) {
        std::cout << "Usage: " << argv[] << " [input]\n";
        return 1;
    }
    unsafe_copy(argv[1]);
    return ;
}

If user_input is longer than 64 bytes, strcpy will write past buffer, corrupting memory and potentially letting an attacker control the program.

Proof of Concept: How Attackers Exploit Memory Corruption

Imagine a browser bug (like those covered by CVE-2023-4584) exists in Firefox’s JavaScript engine. An attacker might use JavaScript to trigger the bug with something like this:

// Fictitious example!
let hugeArray = new Array(100000).fill("A");
try {
    // Assume myVulnerableFunction has a memory bug in old Firefox
    myVulnerableFunction(hugeArray.join(""));
} catch (e) {
    // In vulnerable browsers, this might corrupt memory (not just crash)
}

Such code could be hidden in a regular-looking site or email, and you’d never know.

Note: Actual details are more complex and not shared until everyone has patched.

Thunderbird < 115.2

You are at risk. Anyone opening suspicious websites or emails might be vulnerable.

Update immediately:

- Download Firefox
   - Firefox ESR releases
   - Update Thunderbird

Severity: High

Full Mozilla advisory (with links to specific bug tracker reports):  
- MFSA 2023-29

NIST National Vulnerability Database Entry:  
- CVE-2023-4584

Quick FAQ

Q: Has this been exploited in the wild?  
A: There’s no public report of exploitation yet, but potential is high, and attackers often move fast.

Q: What about add-ons/extensions?  
A: These bugs are in the browser core, not specific add-ons.

Q: Will disabling JavaScript help?  
A: Not always. Some bugs can be triggered by other content (images, fonts, etc.).

Conclusion

CVE-2023-4584 is a reminder that browsers and email clients are huge, complex pieces of software – and that keeping up-to-date is your best defense. If you haven’t updated Firefox or Thunderbird lately, do it now to keep your information and devices secure.

References

- Mozilla Security Advisories
- CVE-2023-4584 at NIST
- Thunderbird Security Center
- Understanding Memory Safety

Timeline

Published on: 09/11/2023 09:15:00 UTC
Last modified on: 09/14/2023 03:45:00 UTC