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
externref
s as arguments from host code to a Wasm function,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
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.
The bug has been fixed, and users should upgrade to Wasmtime 0.30.0.
Additionally, we have updated our primary externref
fuzz target such that it better exercises these code paths and we can have greater confidence in their correctness going forward.
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
.
If you have any questions or comments about this advisory:
bytecodealliance/wasmtime
repository{ "nvd_published_at": "2021-09-17T20:15:00Z", "cwe_ids": [ "CWE-416" ], "severity": "MODERATE", "github_reviewed": true, "github_reviewed_at": "2021-09-17T20:05:21Z" }