WASM Instruction Truncation in Firefox and Thunderbird

CVE-2025-8028

What is CVE-2025-8028?

CVE-2025-8028 is a vulnerability identified within Mozilla's Firefox and Thunderbird applications, which are widely used for web browsing and email communication, respectively. This issue pertains to the WebAssembly (WASM) engine used in these products, specifically involving the br_table instruction on arm64 architecture. The vulnerability arises when the br_table instruction contains an excessive number of entries, leading to a situation where the label associated with the instruction may be truncated. This truncation can result in incorrect calculations of branch addresses, potentially compromising the execution flow of the application. The identified affected versions include Firefox versions prior to 141, various Extended Support Release (ESR) versions, and corresponding versions of Thunderbird.

Potential impact of CVE-2025-8028

1. Execution Flow Manipulation: The truncation of branch addresses might allow attackers to manipulate the execution flow of applications using affected versions of Firefox and Thunderbird. This can lead to unexpected behavior, potentially setting the stage for further exploitation.

2. Increased Attack Surface: By leveraging this vulnerability, an attacker could craft a malicious WASM module that might evade normal checks, thus escalating the opportunity for executing arbitrary code or performing other malicious actions within the context of a user’s browser or email client.

3. System Vulnerability and Data Theft: The presence of this vulnerability could expose sensitive data to unauthorized access or manipulation, particularly if an attacker successfully gains control over the browser or email client being used. As these applications often require privileged access to user data and systems, the implications of exploitation could lead to significant data breaches or malware deployment.

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