WebAssembly (WASM) has become a backbone for innovative web and cloud applications, promising high performance and portability. Tools like wasm2c (which translates WASM binaries into C code) are critical for extending WebAssembly’s reach. However, like any software, wasm2c isn’t immune to vulnerabilities.

CVE-2022-43283 is a vulnerability discovered in wasm2c v1..29 that can cause an unexpected abort of the software due to missing error handling in the CWriter::Write function. This article breaks down what happened, how it works, and what you should do if you use wasm2c.

What is wasm2c?

wasm2c is part of the WebAssembly Binary Toolkit (WABT). Its job is to translate a WebAssembly module into C code, so that it can be compiled using a regular C compiler. This process broadens the usability of WebAssembly modules — especially where running native binaries directly is a challenge.

The Vulnerability: What is CVE-2022-43283?

The problem, officially recorded as CVE-2022-43283, is a security issue found in wasm2c’s version 1..29. The bug is specifically located in the CWriter::Write function, which handles how the tool writes C code output files during conversion.

The issue: If certain conditions are met (like improper or malformed input WASM files), the function triggers an unrecoverable abort. This is because there isn't proper error handling or bounds checking inside CWriter::Write. This means wasm2c can crash unexpectedly, leading to denial-of-service (DoS) conditions if used in automated workflows or server side.

Let's walk through a simplified version of the problematic code

// A simplified snippet based on public sources.
void CWriter::Write(const std::string& content) {
    if (output_file_) {
        fprintf(output_file_, "%s", content.c_str());
    } else {
        // Problem: Instead of handling the error gracefully,
        // the code aborts the entire program!
        abort();  // <-- This is the source of CVE-2022-43283
    }
}

Suppose the output_file_ isn’t correctly initialized (for instance, if the tool fails to open the output file for writing), instead of reporting an error, logging, or providing user feedback, the program abruptly halts with an abort() call.

Why is this bad?

- If wasm2c is running as part of a larger build or deployment pipeline, the entire pipeline may be interrupted.
- In server setups processing untrusted WASM binaries, this could be used for denial-of-service (DoS) attacks.

No sophisticated exploit code is needed. Here's how a shell interaction might look

$ wasm2c mymodule.wasm -o /invalid/path/out.c
# Output:
# Aborted (core dumped)

This can potentially be exploited in environments where users can provide arbitrary WASM modules or output parameters, effectively using wasm2c as a "crash switch".

For those interested in a tangible test, here’s a minimal demonstration in code

# Create an empty wasm module
echo -n '' > empty.wasm

# Try to run wasm2c with invalid output
wasm2c empty.wasm -o /does/not/exist/output.c
# The program will abort with a core dump

On the backend, this calls into the problematic CWriter::Write, which tries to write to an unopened file and triggers the abort.

How Was This Found?

The bug was reported by automated fuzzing and code review. See the original GitHub issue and security advisory:
- Original GitHub Issue (link)
- NVD CVE record

Is There a Patch or Fix?

Yes. The maintainers released a fix after the vulnerability was reported. The updated code checks for a null file pointer and returns an error message instead of calling abort. If you're using wasm2c, update to version 1..31 or later.

Example of the fixed variant

void CWriter::Write(const std::string& content) {
    if (output_file_) {
        fprintf(output_file_, "%s", content.c_str());
    } else {
        // Safer handling: print error, do not abort
        fprintf(stderr, "Error: Output file not open.\n");
        return;
    }
}

References

- CVE-2022-43283 NVD Entry
- WABT Source and Release Announcements
- GitHub Security Advisory
- Original report and discussion thread

Conclusion

CVE-2022-43283 is a classic example of how a small oversight (like handling a null pointer) can cause big reliability and security issues in widely used developer tools. If you’re using wasm2c v1..29 (or below), update right away — and be sure to watch out for similar basic error-handling gaps in other tools you use. If you’re responsible for production workflows, always validate both your inputs and outputs, and keep your toolchains current.

Timeline

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