{"id":"CVE-2026-34945","aliases":["GHSA-m9w2-8782-2946","RUSTSEC-2026-0086"],"url":"https://o3.security/vulnerability/CVE-2026-34945","summary":"Wasmtime leaks host data with 64-bit tables and Winch","details":"### Impact\n\nWasmtime's Winch compiler contains a bug where a 64-bit table, part of the memory64 proposal of WebAssembly, incorrectly translated the `table.size` instruction. This bug could lead to disclosing data on the host's stack to WebAssembly guests. The host's stack can possibly contain sensitive data related to other host-originating operations which is not intended to be disclosed to guests.\n\nThis bug specifically arose from a mistake where the return value of `table.size` was statically typed as a 32-bit integer, as opposed to consulting the table's index type to see how large the returned register could be. When combined with details about Wnich's ABI, such as multi-value returns, this can be combined to read stack data from the host, within a guest. This information disclosure should not be possible in WebAssembly, violates spec semantics, and is a vulnerability in Wasmtime.\n\n### Patches\n\nWasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.\n\n### Workarounds\n\nUsers of Cranelift are not affected by this issue, but users of Winch have no workarounds other than disabling the `Config::wasm_memory64` proposal.","published":"2026-04-09T18:40:48.446Z","modified":"2026-10-28T02:31:05.388839533Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"crates.io","name":"wasmtime","fixedVersion":"36.0.7"},{"ecosystem":"crates.io","name":"wasmtime","fixedVersion":"42.0.2"},{"ecosystem":"crates.io","name":"wasmtime","fixedVersion":"43.0.1"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/34xxx/CVE-2026-34945.json"},{"type":"ADVISORY","url":"https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34945"},{"type":"PACKAGE","url":"https://github.com/bytecodealliance/wasmtime"},{"type":"WEB","url":"https://rustsec.org/advisories/RUSTSEC-2026-0086.html"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:31:05.388839533Z"}}