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 Wasmtimes 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.
The product accesses or uses a pointer that has not been initialized.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Wasmtime | Bytecodealliance | * | 0.33.1 (excluding) |
| Wasmtime | Bytecodealliance | 0.34.0 (including) | 0.34.0 (including) |
If the pointer contains an uninitialized value, then the value might not point to a valid memory location. This could cause the product to read from or write to unexpected memory locations, leading to a denial of service. If the uninitialized pointer is used as a function call, then arbitrary functions could be invoked. If an attacker can influence the portion of uninitialized memory that is contained in the pointer, this weakness could be leveraged to execute code or perform other attacks. Depending on memory layout, associated memory management behaviors, and product operation, the attacker might be able to influence the contents of the uninitialized pointer, thus gaining more fine-grained control of the memory location to be accessed.