CVE-2021-39216 – wasmtime

Package

Manager: pip
Name: wasmtime
Vulnerable Version: >=0 <0.30.0 || >=0 <0.30.0

Severity

Level: Medium

CVSS v3.1: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H

CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N

EPSS: 0.00074 pctl0.22985

Details

Use after free passing `externref`s to Wasm in Wasmtime ### Impact There was a use-after-free bug when passing `externref`s from the host to guest Wasm content. To trigger the bug, you have to explicitly pass multiple `externref`s from the host to a Wasm instance at the same time, either by * passing multiple `externref`s as arguments from host code to a Wasm function, * or returning multiple `externref`s to Wasm from a multi-value return function defined in the host. If you do not have host code that matches one of these shapes, then you are not impacted. If Wasmtime's [`VMExternRefActivationsTable`](https://github.com/bytecodealliance/wasmtime/blob/37c094faf53f1b356aab3c79d451395e4f7edb34/crates/runtime/src/externref.rs#L493) became filled to capacity after passing the first `externref` in, then passing in the second `externref` could trigger a garbage collection. However the first `externref` is not rooted until we pass control to Wasm, and therefore could be reclaimed by the collector if nothing else was holding a reference to it or otherwise keeping it alive. Then, when control was passed to Wasm after the garbage collection, Wasm could use the first `externref`, which at this point has already been freed. We have reason to believe that the effective impact of this bug is relatively small because usage of `externref` is currently quite rare. ### Patches The bug has been fixed, and users should upgrade to Wasmtime 0.30.0. Additionally, we have updated [our primary `externref` fuzz target](https://github.com/bytecodealliance/wasmtime/blob/37c094faf53f1b356aab3c79d451395e4f7edb34/fuzz/fuzz_targets/table_ops.rs) such that it better exercises these code paths and we can have greater confidence in their correctness going forward. ### Workarounds If you cannot upgrade Wasmtime yet, you can avoid the bug by disabling reference types support in Wasmtime by passing `false` to [`wasmtime::Config::wasm_reference_types`](https://docs.rs/wasmtime/0.29.0/wasmtime/struct.Config.html#method.wasm_reference_types). ### References * [The reference types Wasm proposal, which introduces `externref`](https://github.com/WebAssembly/reference-types/) ### 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/)

Metadata

Created: 2021-09-20T19:54:05Z
Modified: 2024-11-19T18:00:37Z
Source: https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/09/GHSA-v4cp-h94r-m7xf/GHSA-v4cp-h94r-m7xf.json
CWE IDs: ["CWE-416"]
Alternative ID: GHSA-v4cp-h94r-m7xf
Finding: F138
Auto approve: 1