CVE-2021-39219
Wrong type for `Linker`-define functions when used across two `Engine`s
Impact
### Impact 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. ### Patches This bug has been patched and users should upgrade to Wasmtime version 0.30.0. ### Workarounds 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`. ### For more information If you have any questions or comments about this advisory: * Reach out to us on [the Bytecode Alliance Zulip chat](https://bytecodealliance.zulipchat.com/#narrow/stream/217126-wasmtime) * Open an issue in [the `bytecodealliance/wasmtime` repository](https://github.com/bytecodealliance/wasmtime/)
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| rust | wasmtime | < 0.30.0 | 0.30.0 |
| pip | wasmtime | >= 0, < 0.30.0 | 0.30.0 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Bytecodealliance | Wasmtime | before 0.30.0 |
| Fedoraproject | Fedora | Versions 34, 35 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://crates.io/crates/wasmtime
- https://github.com/bytecodealliance/wasmtime/commit/b39f087414f27ae40c44449ed5d1154e03449bff
- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-q879-9g95-56mx
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WAVBRYDDUIY2ZR3K3FO4BVYJKIMJ5TP7/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Z2Z33FTXFQ6EOINVEQIP4DFBG53G5XIY/
- https://github.com/advisories/GHSA-q879-9g95-56mx
- https://nvd.nist.gov/vuln/detail/CVE-2021-39219
- https://rustsec.org/advisories/RUSTSEC-2021-0110.html
- https://github.com/bytecodealliance/wasmtime-py/compare/0.29.0...0.30.0
- https://github.com/pypa/advisory-database/tree/main/vulns/wasmtime/PYSEC-2021-322.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