Bug 2006105 (CVE-2021-39219) - CVE-2021-39219 wasmtime: Type confusion vulnerability
Summary: CVE-2021-39219 wasmtime: Type confusion vulnerability
Alias: CVE-2021-39219
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 2006107 2006108 2006109
TreeView+ depends on / blocked
Reported: 2021-09-20 21:15 UTC by Pedro Sampaio
Modified: 2021-09-21 00:21 UTC (History)
2 users (show)

Fixed In Version:
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Last Closed: 2021-09-21 00:21:13 UTC

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Description Pedro Sampaio 2021-09-20 21:15:52 UTC
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`.


Comment 1 Pedro Sampaio 2021-09-20 21:16:42 UTC
Created rust-wasmtime-cache tracking bugs for this issue:

Affects: fedora-34 [bug 2006107]

Created rust-wasmtime-environ tracking bugs for this issue:

Affects: fedora-34 [bug 2006108]

Created rust-wasmtime-fiber tracking bugs for this issue:

Affects: fedora-34 [bug 2006109]

Comment 2 Product Security DevOps Team 2021-09-21 00:21:13 UTC
This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.

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