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-m…
Exact source revision recorded 1 Nov 2026 06:08:01 UTC. It does not establish the source's current position. Latest evidence.
euvd · EUVD-2026-21031
PublishedWasmtime 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.
EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.
Original publisher date fields
datePublished: Apr 9, 2026, 6:48:33 PM
dateUpdated: Apr 10, 2026, 2:12:55 PM
2 related source bulletins · separate from aliases
SUSE-SU-2026:21789-1: Security update for tree-sitter
CVE-2026-34941 · CVE-2026-34942 · CVE-2026-34943 · CVE-2026-34944 · CVE-2026-34945 · CVE-2026-34946 · CVE-2026-34987 · CVE-2026-34988 · CVE-2026-35186 · CVE-2026-35195
openSUSE-SU-2026:20749-1: Security update for tree-sitter
CVE-2026-34941 · CVE-2026-34942 · CVE-2026-34943 · CVE-2026-34944 · CVE-2026-34945 · CVE-2026-34946 · CVE-2026-34987 · CVE-2026-34988 · CVE-2026-35186 · CVE-2026-35195
- Source published
- Apr 9, 2026, 6:48:33 PM (timezone not stated)
- Source modified
- Apr 10, 2026, 2:12:55 PM (timezone not stated)
- Observed here
- 1 Nov 2026 06:08:01 UTC
- Source terms
- ENISA EUVD · source terms and attribution apply
Original source record · Cite this exact observation · Complete original publisher JSON
This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.
EUVD CVSS 4.0 · 9.0 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