CVE-2022-31104 is a medium-severity vulnerability affecting Wasmtime, a standalone runtime for WebAssembly developed by the Bytecode Alliance. The issue lies in the incorrect implementation of two SIMD-related WebAssembly instructions, `i8x16.swizzle` and `select`, specifically on x86_64 architectures. Wasmtime uses Cranelift as its code generator, and the bug originates in Cranelift's instruction lowering phase for these SIMD instructions. For the `swizzle` instruction, the lowering erroneously overwrites the mask input register, potentially corrupting constant values and causing subsequent uses of the same constant to yield incorrect results. For the `select` instruction, when operating on 128-bit vector types (`v128`), the implementation incorrectly moves only the lower 32 bits of the selected input when the condition is zero, leaving the upper 96 bits undefined or containing stale register data. This results in incorrect values being materialized during WebAssembly guest program execution. Although the host environment running Wasmtime is not directly impacted, guest WebAssembly programs may experience unintended branching or incorrect internal values, which could lead to further vulnerabilities such as logic errors or exploitation opportunities arising from miscompilation. The vulnerability affects Wasmtime versions prior to 0.38.1 and Cranelift-codegen versions prior to 0.85.0. The bug is limited to x86_64 hosts; ARM64 (aarch64) and s390x architectures are not affected. Mitigation includes upgrading to the fixed versions or disabling the Wasm SIMD proposal if upgrading is not feasible. No known exploits have been reported in the wild to date.

For European organizations utilizing Wasmtime for WebAssembly execution on x86_64 platforms, this vulnerability could lead to subtle and hard-to-detect errors within guest WebAssembly applications. Such errors may cause incorrect program behavior, including unintended branching and data corruption, which could be exploited by malicious WebAssembly modules to bypass security controls or cause denial of service within the guest environment. While the host system's confidentiality, integrity, and availability are not directly compromised, the integrity of applications relying on Wasmtime could be undermined, potentially affecting critical services that embed WebAssembly for sandboxed execution, such as cloud platforms, edge computing, and serverless environments. Given the increasing adoption of WebAssembly in cloud-native and edge scenarios, this vulnerability could impact sectors like finance, telecommunications, and critical infrastructure where Wasmtime is integrated. The lack of known exploits reduces immediate risk, but the potential for exploitation through crafted WebAssembly modules necessitates prompt remediation to maintain application correctness and security.

1. Upgrade Wasmtime to version 0.38.1 or later and Cranelift-codegen to version 0.85.0 or later to apply the corrected instruction lowerings. 2. If upgrading is not immediately possible, disable the WebAssembly SIMD proposal in Wasmtime configurations to avoid triggering the vulnerable code paths. 3. Audit and test WebAssembly guest applications running on affected Wasmtime versions for anomalous behavior or incorrect outputs that could indicate exploitation or manifestation of the bug. 4. Implement strict input validation and sandboxing controls on WebAssembly modules to limit the risk of malicious modules exploiting this vulnerability. 5. Monitor Wasmtime and Cranelift project updates and security advisories for any further patches or related vulnerabilities. 6. For organizations deploying Wasmtime in production, incorporate this vulnerability into risk assessments and incident response plans, emphasizing the importance of timely patching and configuration management.