In February 2024, Mozilla disclosed CVE-2024-1552, a vulnerability affecting some of their most popular products: Firefox, Firefox ESR, and Thunderbird. This bug is exclusive to 32-bit ARM devices and roots from a problem with incorrect code generation that can lead to unexpected numeric conversions. Simply put, the browser might mishandle numbers in some cases, causing unpredictable — and sometimes exploitable — behavior.

This post breaks down the details of the vulnerability, shows a simplified code example, discusses how it could be exploited, and offers references and mitigation advice.

What is CVE-2024-1552?

At a low level, software often converts numbers between different types (like from a 64-bit float to a 32-bit integer). Compilers generate machine code for these operations. In this case, on 32-bit ARM chips, certain number conversions weren’t compiled right, leading to:

Possible security exploits

Mozilla marked this as a high-severity bug, since it can only happen on 32-bit ARM and not on other architectures.

> Affected versions:
> - Firefox below 123
> - Firefox ESR below 115.8
> - Thunderbird below 115.8

Simple Code Example

Imagine you have a value that’s a floating-point number (double), and you want to cast it to an integer. Usually, the compiler turns your code into machine instructions that do this safely. With the bug, the compiled code on 32-bit ARM might go wrong.

JavaScript Example (for context)

function unsafeConvert(num) {
    let intNum = num | ; // force conversion to 32-bit int
    return intNum;
}

let suspicious = Math.pow(2, 42); // way bigger than 32-bit max!
console.log(unsafeConvert(suspicious));

Expected: Since suspicious is too big for a 32-bit int, most systems truncate or return .

With the flawed ARM codegen: The browser might do a bogus conversion, resulting in memory corruption or even letting a crafted web page perform unintended actions.

C Example (hypothetical, low-level)

double val = 214748365.; // slightly bigger than 2^31
int32_t weird = val; // buggy conversion on 32-bit ARM!
printf("%d\n", weird);

In-depth Exploit Scenario

Most bugs in type conversion don’t go beyond crashes — but in highly dynamic environments like a browser or email program, attackers can try to abuse these conversions for memory manipulation.

Drive-by JavaScript:

- An attacker hosts JavaScript that passes massive or weirdly-crafted floats into tricky functions, hoping to trigger the wrong conversion.

Shape Memory or Type Confusion:

- If the conversion leaks into the memory allocator or object's shape tags, it could allow the attacker to write in-memory pointers, changing what the browser does in later code.
3. Plant Shellcode / Info Leak:
- If they get write-what-where or misread data, it’s a classic step towards code execution or leaking secrets.

Public exploit code: At the time of this writing, there are no full public exploits, but this type of bug is often used in exploit chains, especially when attackers know their victims use 32-bit ARM (think cheap Android devices or Raspberry Pi browsers).

Official References

- Mozilla Security Advisory 2024-13
- Bugzilla report

Users

- Update now. Make sure you’ve installed Firefox 123 or later (or for ESR/Thunderbird, at least 115.8). This closes the hole.

Enterprises

- Audit devices. If you distribute software to ARM-based devices (Android, IoT), double-check all browser versions.

Conclusion

CVE-2024-1552 is a classic example of a platform-specific vulnerability with potentially serious consequences.
It’s a rare bug that only bites on certain hardware, but if you or your users use 32-bit ARM devices (Raspberry Pi, old Androids, some smart TVs), update Firefox, ESR, or Thunderbird immediately.

While no public attacks are known at publishing, skilled attackers often chain such bugs, and browser vulnerabilities remain a top target. Staying up-to-date is your best line of defense.


*This post has been exclusively prepared to explain CVE-2024-1552 in plain language for technical and non-technical readers alike. For more technical details, see the original Mozilla bugzilla ticket and advisory.*

Timeline

Published on: 02/20/2024 14:15:08 UTC
Last modified on: 12/10/2024 17:46:14 UTC