CVE-2021-39219

Date: September 17, 2021

Wasmtime is an open source runtime for WebAssembly & WASI. Wasmtime before version 0.30.0 is affected by a type confusion vulnerability. As a Rust library the "wasmtime" crate clearly marks which functions are safe and which are "unsafe", guaranteeing that if consumers never use "unsafe" then it should not be possible to have memory unsafety issues in their embeddings of Wasmtime. An issue was discovered in the safe API of "Linker::func_*" APIs. These APIs were previously not sound when one "Engine" was used to create the "Linker" and then a different "Engine" was used to create a "Store" and then the "Linker" was used to instantiate a module into that "Store". Cross-"Engine" usage of functions is not supported in Wasmtime and this can result in type confusion of function pointers, resulting in being able to safely call a function with the wrong type. Triggering this bug requires using at least two "Engine" values in an embedding and then additionally using two different values with a "Linker" (one at the creation time of the "Linker" and another when instantiating a module with the "Linker"). It's expected that usage of more-than-one "Engine" in an embedding is relatively rare since an "Engine" is intended to be a globally shared resource, so the expectation is that the impact of this issue is relatively small. The fix implemented is to change this behavior to "panic!()" in Rust instead of silently allowing it. Using different "Engine" instances with a "Linker" is a programmer bug that "wasmtime" catches at runtime. This bug has been patched and users should upgrade to Wasmtime version 0.30.0. If you cannot upgrade Wasmtime and are using more than one "Engine" in your embedding it's recommended to instead use only one "Engine" for the entire program if possible. An "Engine" is designed to be a globally shared resource that is suitable to have only one for the lifetime of an entire process. If using multiple "Engine"s is required then code should be audited to ensure that "Linker" is only used with one "Engine".

Language: RUST