CVE-2021-39218

Description

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`.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

References

• https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-4873-36h9-wv49
• https://nvd.nist.gov/vuln/detail/CVE-2021-39218
• https://github.com/bytecodealliance/wasmtime/commit/398a73f0dd862dbe703212ebae8e34036a18c11c
• https://crates.io/crates/wasmtime
• https://github.com/bytecodealliance/wasmtime
• https://github.com/bytecodealliance/wasmtime-py/compare/0.29.0...0.30.0
• https://github.com/pypa/advisory-database/tree/main/vulns/wasmtime/PYSEC-2021-321.yaml
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WAVBRYDDUIY2ZR3K3FO4BVYJKIMJ5TP7
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/Z2Z33FTXFQ6EOINVEQIP4DFBG53G5XIY
• https://rustsec.org/advisories/RUSTSEC-2021-0110.html
• https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-q879-9g95-56mx
• https://nvd.nist.gov/vuln/detail/CVE-2021-39219
• https://github.com/bytecodealliance/wasmtime/commit/b39f087414f27ae40c44449ed5d1154e03449bff
• https://github.com/pypa/advisory-database/tree/main/vulns/wasmtime/PYSEC-2021-322.yaml
• https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-v4cp-h94r-m7xf
• https://nvd.nist.gov/vuln/detail/CVE-2021-39216
• https://github.com/bytecodealliance/wasmtime/commit/101998733b74624cbd348a2366d05760b40181f3
• https://github.com/pypa/advisory-database/tree/main/vulns/wasmtime/PYSEC-2021-320.yaml
• https://security-tracker.debian.org/tracker/CVE-2021-39218