A new vulnerability (CVE-2022-43283) has been identified in wasm2c v1..29, a widely used tool for translating WebAssembly (Wasm) code into C code. This vulnerability specifically affects the CWriter::Write function, which, under specific conditions, might lead to the execution of an abort() calls. In this post, we will provide an in-depth analysis of the vulnerability, present a code snippet highlighting the issue, and detail the potential exploit scenarios. Ultimately, we aim to empower developers with the knowledge necessary to mitigate this specific risk.

Origins of the Vulnerability

WebAssembly (Wasm) is an open standard that defines a binary format and a corresponding assembly-like text format for executable code in web pages. To simplify the process of compiling and running Wasm code in non-web environments, tools like wasm2c are often employed. Wasm2c is part of the WebAssembly Binary Toolkit (WABT) and converts WebAssembly binary files to C code that can subsequently be compiled and executed natively. The vulnerability in question, CVE-2022-43283, affects wasm2c version 1..29.

Vulnerability Details

This vulnerability resides in the CWriter::Write function when handling specific inputs, causing the program to execute the abort() system call. The abort() function is intended to terminate a program immediately and generate a core dump file in certain debugging scenarios.

Code Snippet

Here's a simplified snippet of code from the src/wasm2c.cc file within wasm2c v1..29, highlighting the vulnerable part of the CWriter::Write function:

void CWriter::Write() {
  ...
  for (const ElemSegment& segment : module->elem_segments) {
    ...
    stream_ << "_wasm_instance.instance.";
    ...
    if (segment.table_var.is_none()) {
      stream_ << "elem->table.";
      table_index = ;
    } else {
      stream_ << "elem->table_" << table_index++ << "->";
    }
    stream_ << "table";
    if (auto* elem_desc = segment.elem_desc.get()) {
      ...
      for (const Expr& elem_expr : elem_desc->elem_exprs) {
        stream_ << ",";
        ...
        switch (opcode) {
          ...
          default:
            stream_ << "WASM_RT_TRAP(";
            WriteTrapReason(static_cast<TrapReason>(opcode));
            stream_ << ")";
            abort();
        }
        ...
      }
    }
  }
  ...
}

In the snippet above, an abort() is executed in the default case when none of the matching conditions are met. When the abort() call occurs, it triggers a program termination and might create undesired side effects or enable exploitation by malicious actors.

Exploit Scenarios

While most use cases involving wasm2c are focused on compiling trusted WebAssembly code, a malicious actor could potentially execute a denial-of-service (DoS) attack. By exploiting the vulnerability found in CWriter::Write, the attacker could cause the program to unexpectedly terminate, which would disrupt the compilation process.

Mitigation and References

Upstream developers have acknowledged the vulnerability and are working on a patch. It is strongly advised to pay close attention to the official WABT GitHub repository for updates and releases addressing CVE-2022-43283: https://github.com/WebAssembly/wabt

Conclusion

This blog post provides an insight into the CVE-2022-43283 vulnerability, which affects wasm2c v1..29 by causing an abort() call in the CWriter::Write function. Developers are strongly encouraged to keep an eye on official updates and apply the appropriate patches as soon as they become available. Maintaining robust software security procedures is crucial for safeguarding against both known and unknown vulnerabilities.

Timeline

Published on: 10/28/2022 21:15:00 UTC
Last modified on: 11/01/2022 17:21:00 UTC