CVE-2026-34987— Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access

Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access

Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime with its Winch (baseline) non-default compiler backend may allow properly constructed guest Wasm to access host memory outside of its linear-memory sandbox. This vulnerability requires use of the Winch compiler (-Ccompiler=winch). By default, Wasmtime uses its Cranelift backend, not Winch. With Winch, the same incorrect assumption is present in theory on both aarch64 and x86-64. The aarch64 case has an observed-working proof of concept, while the x86-64 case is theoretical and may not be reachable in practice. This Winch compiler bug can allow the Wasm guest to access memory before or after the linear-memory region, independently of whether pre- or post-guard regions are configured. The accessible range in the initial bug proof-of-concept is up to 32KiB before the start of memory, or ~4GiB after the start of memory, independently of the size of pre- or post-guard regions or the use of explicit or guard-region-based bounds checking. However, the underlying bug assumes a 32-bit memory offset stored in a 64-bit register has its upper bits cleared when it may not, and so closely related variants of the initial proof-of-concept may be able to access truly arbitrary memory in-process. This could result in a host process segmentation fault (DoS), an arbitrary data leak from the host process, or with a write, potentially an arbitrary RCE. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

跨界内存读

wasmtime 缓冲区错误漏洞

wasmtime是Bytecode Alliance开源的一个轻量级WebAssembly运行时。 Wasmtime 36.0.7之前版本、42.0.2之前版本和43.0.1之前版本存在缓冲区错误漏洞，该漏洞源于Winch编译器后端存在缺陷，可能导致访客Wasm访问其线性内存沙箱之外的主机内存，造成拒绝服务、数据泄露或潜在的远程代码执行。

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