---
title: Wasmtime fixes two CVSS 9.9 sandbox escapes in its Cranelift compiler, one hitting every aarch64 build since 2020 | ctxsec
url: https://ctxsec.com/items/wasmtime-cranelift-two-critical-sandbox-escapes
description: ""
status: "confirmed (Wasmtime advisories GHSA-897f-g5gm-fmxm and GHSA-mghf-wjfp-p5xm, Oct 19; added to GitHub's advisory database Oct 23); no exploitation reported"
published: 2026-10-23
---

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[← Cybersecurity News](/news) · [markdown](/items/wasmtime-cranelift-two-critical-sandbox-escapes.md)

confirmed (Wasmtime advisories GHSA-897f-g5gm-fmxm and GHSA-mghf-wjfp-p5xm, Oct 19; added to GitHub's advisory database Oct 23); no exploitation reported

2026-10-23

### Wasmtime fixes two CVSS 9.9 sandbox escapes in its Cranelift compiler, one hitting every aarch64 build since 2020

If you use Wasmtime to run untrusted WebAssembly (plugins, serverless functions, or tool code from agents), a malicious module can break out of the sandbox with default settings. Both bugs are rated **CVSS 9.9**:

- **CVE-2026-115889**: Cranelift packed its internal value indices too tightly. A huge or specially built Wasm function can overflow them silently in release builds, causing miscompilation and a sandbox escape on any platform. Wasmtime 43 and later are not affected. Older lines are fixed in **36.0.19**.
- **CVE-2026-115893**: on **aarch64**, a `br_table` with more than about 256k targets can compile to a wrong branch target, letting the module jump to code at an offset it controls. This affects every Wasmtime version with aarch64 support since 2020. Fixed in **36.0.19, 48.0.7 and 49.0.4** (50.0.0 is also out).

Upgrade, and check for embedded copies: many Rust projects vendor Wasmtime, so run `cargo tree -i wasmtime` or check your SBOM. The project has not reported any exploitation.

Sources: [Wasmtime advisory GHSA-897f-g5gm-fmxm (CVE-2026-115889)](https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm) · [Wasmtime advisory GHSA-mghf-wjfp-p5xm (CVE-2026-115893)](https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-mghf-wjfp-p5xm) · [Wasmtime releases](https://github.com/bytecodealliance/wasmtime/releases)