{"id":"CVE-2026-34987","revision":"82f46494dd1c42f5946e3dce11c7e03b","records":[{"revision":"82f46494dd1c42f5946e3dce11c7e03b","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-34987","aliases":[],"title":"Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access","description":"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.","state":0,"publishedAt":"2026-04-09T18:48:33.552+00:00","modifiedAt":"2026-04-10T14:12:55.374+00:00","affected":[{"ecosystem":"Vendor product","name":"wasmtime","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"bytecodealliance\",\n                    \"product\": \"wasmtime\",\n                    \"versions\": [\n                        {\n                            \"version\": \">= 25.0.0, < 36.0.7\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \">= 37.0.0, < 42.0.2\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \">= 43.0.0, < 44.0.1\",\n                            \"status\": \"affected\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"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","score":9,"severity":"CRITICAL"}],"references":["https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-xx5w-cvp6-jv83"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-34987","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-34987","identifiers":["CVE-2026-34987"]},"retained":false,"historicalAffected":[]}],"coverage":[]}