Panic in Wasmtime: Type Mismatch Vulnerability
Summary
RUSTSEC-2026-0355: Panic viewing component model stream or future as the wrong type. Affects wasmtime across 2 version ranges.
>= 46.0.0, < 48.0.6
>= 49.0.0, < 49.0.3
Fixed in 48.0.6 or 49.0.3, depending on the release line you run. How to fix ↓
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Background
Wasmtime is a standalone JIT (Just-In-Time) compiler for WebAssembly, designed to execute WebAssembly modules efficiently and securely. It provides a powerful runtime environment for running WebAssembly code, making it a popular choice for developers looking to integrate WebAssembly into their applications. However, a recent vulnerability has been identified that allows for panic conditions when viewing component model streams or futures as incorrect types, potentially leading to application crashes and unexpected behavior.
Vulnerability Detail
The vulnerability arises from a type mismatch when handling component model streams or futures within the Wasmtime package. This issue can lead to panic situations, where the application may crash unexpectedly if the wrong type is viewed. The vulnerability is particularly concerning as it can be exploited in scenarios where type safety is critical, potentially leading to denial of service or other unintended consequences. The affected versions include 46.0.0 to 48.0.6 and 49.0.0 to 49.0.3, with the vulnerability documented in the RustSec database and associated with the GitHub security advisory GHSA-63h4-6cx9-pjfj.
How To Fix
Latest published version: 50.0.0 as of 22 Oct 2026
Upgrading to it may include breaking changes; the versions below are the minimum fixed release for this vulnerability.
If you can't move to the latest
The minimum fixed version depends on the release line you run.
-
>= 46.0.0, < 48.0.648.0.6 -
>= 49.0.0, < 49.0.349.0.3
Tip — Not sure which release line you're on? Vulert can find the fix for the version you are using. Scan free →
Workaround
As a temporary workaround, ensure that you are validating the types of streams and futures before processing them. Implement additional checks in your code to prevent type mismatches that could lead to panic situations. For example:
if let Some(valid_stream) = stream.downcast_ref::<ExpectedType>() {
// Process valid stream
} else {
// Handle type mismatch gracefully
}
Conclusion
The Wasmtime package has a significant vulnerability related to type mismatches in component model streams and futures, which can lead to panic conditions. It is crucial for developers using affected versions to update to the latest patched versions to ensure the stability and security of their applications. Implementing type validation can serve as a temporary workaround while updates are being applied.
See every vulnerability recorded for wasmtime →
FAQ
The affected versions are 46.0.0 to 48.0.6 and 49.0.0 to 49.0.3.
The CVSS score of this vulnerability is 5.9.
You can use Vulert to monitor and alert for open-source vulnerabilities in your software. Visit the Vulert playground at Vulert Scanner to check if your application is affected without any signup.
If you cannot update immediately, implement type validation checks in your code to avoid panic situations caused by type mismatches.
More information can be found in the GitHub security advisory at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-63h4-6cx9-pjfj.
References
Related vulnerabilities
Recent vulnerabilities recorded for wasmtime.
