The Common Vulnerabilities and Exposures (CVE) system recently identified a critical vulnerability within the ARM64 Ion compiler, known as CVE-2023-29548. The improper lowering instruction affects popular Mozilla products like Firefox, Focus for Android, Firefox ESR, Firefox for Android, and Thunderbird. In this article, we'll delve into the details of this vulnerability, provide snippets of the affected code, and discuss potential exploits attackers can follow. Finally, we'll provide a summary of the software versions impacted and explain how users can protect themselves.

Vulnerability Details

The ARM64 Ion compiler is a fundamental component of the JavaScript Just-in-Time (JIT) compiler for ARM64 systems. It is responsible for converting high-level JavaScript code into low-level, optimal machine code, which is ultimately executed by the system. In this case, the compiler possesses a "wrong lowering" instruction that generates incorrect output for optimized code. This miscalculation opens the door to potential exploits and security risks.

Here's a brief code snippet displaying the incorrect conversion

// Problematic lowering instruction
if (operand2.kind() == Operand::kConstant)
  ScratchRegisterScope temps(this);
  Register scratch = temps.AcquireW();
  uint32_t constOperand = operand2.Immediate32();
  mov(scratch, Operand(constOperand));
  Ssat(result, saturate_to_bits, operand1.W(), scratch);

The issue occurs when the compiler incorrectly handles the conversion of certain JavaScript operations, generating an improper output that can be read by a malicious actor.

Exploits and Risks

An attacker skilled enough to identify this vulnerability could unleash several types of exploits to compromise users' systems and hijack their data. Some potential attack scenarios are:

1. Browser-based attacks: Compromise users' protected information and perform actions on their behalf by inserting malicious payloads via malevolent ads or websites.
2. Email attacks: Deliver malicious content within an email that takes advantage of the vulnerability when opened in Thunderbird, compromising sensitive information.
3. Android-based attacks: Infiltrate Android-based Mozilla apps (Firefox or Focus) to siphon off user data and compromise phone security.

Thunderbird < 102.10

To determine your software version, check the 'About' menu of the specific Mozilla product or app.

How to Protect Yourself

To mitigate the dangers associated with this vulnerability, Mozilla recommends updating all impacted software to the latest version. Users can typically do this by following the in-program update prompts or by downloading the latest release from Mozilla’s website.


CVE-2023-29548 exposes a critical vulnerability in Mozilla products that can have severe implications for users' privacy, security, and data integrity. Understanding the impact of such an issue and taking the necessary precautions to stay safe and updated is vital. Stay vigilant and update your apps to ensure the protection of your sensitive data and the security of your systems.


Published on: 06/02/2023 17:15:00 UTC
Last modified on: 06/09/2023 03:56:00 UTC