CVE-2022-31146 is a use-after-free vulnerability (CWE-416) found in Wasmtime, a standalone runtime for WebAssembly developed by the Bytecode Alliance. The vulnerability stems from a bug in Wasmtime's code generator, Cranelift, specifically related to the handling of reference types during garbage collection (GC). In versions of Wasmtime from 0.37.0 up to but not including 0.38.2, and from 0.84.0 up to but not including 0.85.2, functions that use WebAssembly reference types may lack the necessary metadata for the runtime GC to correctly identify live references. As a result, the GC may erroneously reclaim and deallocate memory that is still in use by these functions. When the function continues execution, it accesses memory that has already been freed, leading to a use-after-free condition. This can cause undefined behavior including crashes, memory corruption, or potentially arbitrary code execution depending on the context of the memory usage. The root cause was introduced during the migration to the regalloc2 register allocator in Wasmtime 0.37.0. The vulnerability has been patched in Wasmtime 0.38.2 and 0.85.2. Mitigations include disabling the reference types feature by setting `wasmtime::Config::wasm_reference_types` to false or downgrading to Wasmtime 0.36.0 or earlier. No known exploits in the wild have been reported to date. The vulnerability requires the use of WebAssembly modules that utilize reference types and the Wasmtime runtime configured to enable them. Exploitation does not require user interaction but does require the ability to execute or load crafted WebAssembly code within the vulnerable Wasmtime runtime environment.

For European organizations, the impact of this vulnerability depends largely on the extent to which Wasmtime is used in their software stacks, particularly in environments running WebAssembly workloads. Wasmtime is increasingly adopted in cloud-native applications, edge computing, and serverless platforms due to its lightweight and secure runtime characteristics. A successful exploitation could lead to denial of service through crashes or memory corruption, potentially disrupting critical services. More severe impacts could include arbitrary code execution, which would compromise confidentiality and integrity of data and systems. This is particularly concerning for sectors relying on WebAssembly for sandboxed execution of untrusted code, such as financial services, telecommunications, and critical infrastructure. Given the vulnerability affects runtime garbage collection of reference types, applications using advanced WebAssembly features are more at risk. The absence of known exploits reduces immediate risk, but the medium severity rating and the potential for exploitation in multi-tenant or cloud environments warrant proactive mitigation. Organizations using Wasmtime in production should prioritize patching to avoid exposure to memory corruption vulnerabilities that can be leveraged for privilege escalation or persistent compromise.

1. Upgrade Wasmtime to version 0.38.2 or later (for the 0.37.x branch) or 0.85.2 or later (for the 0.84.x branch) to apply the official patch addressing this vulnerability. 2. If immediate upgrading is not feasible, disable the WebAssembly reference types feature by setting `wasmtime::Config::wasm_reference_types` to false, effectively preventing the vulnerable code path from being exercised. 3. Consider downgrading to Wasmtime 0.36.0 or earlier as a temporary workaround, though this may impact functionality and compatibility with newer WebAssembly modules. 4. Audit and monitor WebAssembly workloads for unusual behavior or crashes that could indicate exploitation attempts. 5. Implement runtime memory protection and sandboxing measures around Wasmtime instances to limit the impact of potential memory corruption. 6. For organizations deploying Wasmtime in multi-tenant or cloud environments, enforce strict input validation and isolation to prevent untrusted WebAssembly modules from triggering the vulnerability. 7. Maintain an inventory of systems and applications using Wasmtime to ensure timely patching and configuration management. 8. Engage with Wasmtime and Bytecode Alliance community channels for updates and best practices related to WebAssembly security.