Wasmtime CVE-2026-115889 and CVE-2026-115893 (CVSS 9.9): Cranelift miscompilation lets a malicious Wasm module escape the sandbox. Which Wasmtime versions are fixed?

What it is: the Bytecode Alliance published two critical Wasmtime advisories on October 19, 2026. Both are bugs in the Cranelift compiler backend that let a specially built WebAssembly module get miscompiled and break out of the Wasm sandbox into the host process. - CVE-2026-115889: an overflow in how Cranelift packs internal value indices, affecting all CPU architectures in Wasmtime releases before 43. - CVE-2026-115893: a wrong branch target for very large br_table instructions, affecting only aarch64 (ARM64) hosts using the default Cranelift backend. Am I affected: - You are exposed if you run WebAssembly you don't fully trust (plugins, user-submitted code, multi-tenant serverless or edge functions, agent tool sandboxes) on an affected Wasmtime with Cranelift. If every module you run is your own trusted code, the risk is much lower, but upgrade anyway. - Check the version: cargo tree -i wasmtime (Rust), the wasmtime package version in Python (pip show wasmtime), Go, .NET or Node bindings, or wasmtime --version for the CLI. Also check products that embed Wasmtime (proxies, serverless platforms, databases and plugin hosts) for vendor updates. Fix: upgrade to a patched release that covers both flaws: 36.0.19 (LTS line), 48.0.7, 49.0.4, or 50.0.0 and later. Release lines other than these (for example 37 to 47) are not listed as patched, so move to a supported fixed line. Rebuild and redeploy anything that statically links Wasmtime; for language bindings, update the binding package to the version built on a fixed Wasmtime. Interim mitigation until you can upgrade: stop running untrusted modules, or run the Wasm host inside an additional OS-level sandbox (separate low-privilege process, container or VM, no secrets in its environment) so a sandbox escape doesn't reach anything valuable. If you cache precompiled modules (.cwasm), recompile them with the fixed version, because the bug is in the generated code. After: confirm the deployed version, clear and rebuild compiled-module caches, and review hosts that ran untrusted modules for unexpected processes, file access or outbound connections. Sources: https://thehackernews.com/2026/10/two-critical-wasmtime-flaws-could-let.html https://advisories.gitlab.com/cargo/wasmtime/CVE-2026-115889/ https://vuldb.com/cve/CVE-2026-115893