{"schemaVersion":3,"id":"CVE-2026-34987","aliases":["UBUNTU-CVE-2026-34987","DEBIAN-CVE-2026-34987","CGA-3hg6-r4j7-qpj5","CGA-485j-qjqw-ccgp","CGA-5wc8-5882-x2wv","CGA-66g4-73vj-8q35","CGA-c6vr-2m75-j7r9","CGA-g8h8-gwwv-wmwc","CGA-h494-2cgq-h92c","CGA-q96q-c7gx-g3h7","CGA-vh9p-p2gw-43v5","CGA-wmmw-23fh-h2c6","GHSA-xx5w-cvp6-jv83","RUSTSEC-2026-0095"],"status":"published","duplicateOf":null,"title":null,"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.","dates":{"published":"2026-04-09T18:48:33.552Z","modified":"2026-04-10T14:12:55.374Z","reserved":null,"kevAdded":[],"kevDue":[]},"cvss":{"headline":{"score":9.9,"severity":"critical","version":"3.1","versionLabel":"v3.1","source":"NVD","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","computed":false,"selection":"backend-summary"},"metrics":[{"version":"4.0","versionLabel":"v4.0","source":"CVE.org","score":9,"severity":"critical","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","exploitability":null,"impact":null,"computed":false},{"version":"4.0","versionLabel":"v4.0","source":"OSV · Ubuntu","score":9,"severity":"critical","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","exploitability":null,"impact":null,"computed":true},{"version":"3.1","versionLabel":"v3.1","source":"OSV · 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