Invalid drop of partially-initialized instances in wasmtime

Summary

Wasmtime is an open source runtime for WebAssembly & WASI. Prior to versions 0.34.1 and 0.33.1, there exists a bug in the pooling instance allocator in Wasmtime's runtime where a failure to instantiate an instance for a module that defines an `externref` global will result in an invalid drop of a `VMExternRef` via an uninitialized pointer. A number of conditions listed in the GitHub Security Advisory must be true in order for an instance to be vulnerable to this issue. Maintainers believe that the effective impact of this bug is relatively small because the usage of `externref` is still uncommon and without a resource limiter configured on the `Store`, which is not the default configuration, it is only possible to trigger the bug from an error returned by `mprotect` or `VirtualAlloc`. Note that on Linux with the `uffd` feature enabled, it is only possible to trigger the bug from a resource limiter as the call to `mprotect` is skipped. The bug has been fixed in 0.34.1 and 0.33.1 and users are encouraged to upgrade as soon as possible. If it is not possible to upgrade to version 0.34.1 or 0.33.1 of the `wasmtime` crate, it is recommend that support for the reference types proposal be disabled by passing `false` to `Config::wasm_reference_types`. Doing so will prevent modules that use `externref` from being loaded entirely.

Timeline

1. Feb 16, 2022, 10:00 PM UTCCVE published
2. Apr 23, 2025, 2:10 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Apr 23, 2025, 7:03 PM UTCRecord last updated

Affected versions

• bytecodealliance wasmtime

  fixed in 0.33.0

• wasmtimecrates.io

  From 0.0.0-0 · fixed in 0.38.2

• wasmtimecrates.io

  From 0.34.0 · fixed in 0.34.1

• wasmtimecrates.io

  fixed in 0.33.1

• wasmtimecrates.io

  fixed in 0.38.2

• cranelift-codegencrates.io

  fixed in 0.85.2

• wasmtimecrates.io

  From 0.0.0-0 · fixed in 0.33.1; From 0.34.0 · fixed in 0.34.1

References 3