CVE-2025-1933: Critical Vulnerability in JIT Compiler for WASM i32 Return Values on 64-bit CPUs

CVE-2025-1933 is a critical vulnerability discovered in the Just-In-Time (JIT) compiler for WebAssembly (WASM) running on 64-bit CPUs. Specifically, this vulnerability affects the way JIT compiles i32 return values, which can sometimes pick up bits from the leftover memory and ultimately cause these values to be treated as a different data type. This security flaw impacts multiple Mozilla products, including Firefox, Firefox ESR, and Thunderbird.

In this post, we will provide you with a comprehensive overview of CVE-2025-1933, including the affected software versions, a code snippet illustrating the issue, exploit details, and links to original references. We will also offer potential mitigation strategies to help you protect your systems from this dangerous vulnerability.

Code Snippet

The following code snippet demonstrates a simple WebAssembly module that illustrates the issue with JIT compilation of i32 return values:

(module
  (func $getMemoryValue (result i32)
    (i32.load8_s (i32.const ))
  )
  (memory 1)
  (export "getMemoryValue" (func $getMemoryValue))
)

In this example, the WebAssembly module defines a simple function $getMemoryValue that reads a signed 8-bit integer from memory at offset and returns it as a 32-bit integer (i32). When this code is executed on a 64-bit CPU using a vulnerable JIT compiler, it might pick up extra bits from leftover memory, causing the returned value to be treated incorrectly.

Exploit Details

An attacker could exploit this vulnerability by crafting a malicious WebAssembly module designed to trigger the vulnerability, such as the one shown above. The attacker would then need to convince the user to visit a website hosting the malicious WebAssembly module or view an email message containing the malicious code in Thunderbird.

Once the malicious code has been executed, the attacker can potentially leverage the incorrect interpretation of the i32 return values to bypass security checks or cause the application to crash, leading to a Denial of Service (DoS) condition. In some cases, the attacker could also execute arbitrary code on an affected system, granting them complete control over the targeted machine.

For more detailed information about CVE-2025-1933, consult the following references

- Mozilla Security Advisory
- CVE-2025-1933 Record in NIST National Vulnerability Database
- OWASP WebAssembly Security

Mitigation Strategies

To protect your systems from being exploited by CVE-2025-1933, you should immediately upgrade the affected software to their latest versions:

Update Thunderbird to version 128.8 or later

Furthermore, ensure that you follow general best practices for securing web browsers and email clients, such as not visiting untrusted websites and avoiding opening suspicious email attachments or links.

Conclusion

CVE-2025-1933 is a critical vulnerability that poses a significant risk to users of Mozilla Firefox, Firefox ESR, and Thunderbird on 64-bit CPUs. By taking the necessary precautions and staying vigilant, you can effectively protect your systems and prevent attackers from exploiting this dangerous security flaw.

Timeline

Published on: 03/04/2025 14:15:38 UTC
Last modified on: 03/25/2025 14:15:27 UTC