{"id":"JLSEC-2026-1358","summary":"Wasmtime has host data leakage 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.","modified":"2026-08-21T21:14:21.990857996Z","published":"2026-08-21T20:43:33.133Z","upstream":["CVE-2026-34945","EUVD-2026-21024","GHSA-m9w2-8782-2946"],"database_specific":{"license":"CC-BY-4.0","sources":[{"url":"https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-34945","html_url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34945","database_specific":{"status":"Analyzed"},"affected":{"bytecodealliance:wasmtime":["\u003e= 25.0.0, \u003c 36.0.7","\u003e= 37.0.0, \u003c 42.0.2","\u003e= 43.0.0, \u003c 43.0.1"]},"id":"CVE-2026-34945","imported":"2026-08-21T20:09:02.077Z","modified":"2026-06-17T10:39:51.837Z","published":"2026-04-09T19:16:24.330Z"},{"id":"GHSA-m9w2-8782-2946","imported":"2026-08-21T20:09:07.150Z","modified":"2026-04-24T21:03:34Z","published":"2026-04-09T20:23:02Z","url":"https://api.github.com/advisories/GHSA-m9w2-8782-2946","html_url":"https://github.com/advisories/GHSA-m9w2-8782-2946"},{"affected":{"bytecodealliance:wasmtime":["25.0.0, \u003c 36.0.7","37.0.0, \u003c 42.0.2","43.0.0, \u003c 44.0.1"]},"id":"EUVD-2026-21024","imported":"2026-08-21T20:09:03.523Z","modified":"2026-04-10T14:12:18Z","published":"2026-04-09T18:40:48Z","url":"https://euvdservices.enisa.europa.eu/api/enisaid?id=EUVD-2026-21024","html_url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-21024"}]},"references":[{"type":"WEB","url":"https://github.com/advisories/GHSA-m9w2-8782-2946"},{"type":"WEB","url":"https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946"},{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-34945"},{"type":"WEB","url":"https://rustsec.org/advisories/RUSTSEC-2026-0086.html"}],"affected":[{"package":{"name":"Wasmtime_jll","ecosystem":"Julia","purl":"pkg:julia/Wasmtime_jll?uuid=d20e7296-4f3e-515c-90b9-d2595a77bf72"},"ranges":[{"type":"SEMVER","events":[{"introduced":"39.0.0+0"},{"fixed":"45.0.1+0"}]}],"database_specific":{"source":"https://github.com/JuliaLang/SecurityAdvisories.jl/tree/generated/osv/2026/JLSEC-2026-1358.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N","source":"NVD"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","source":"CNA"}],"credits":[{"name":"alexcrichton","contact":["https://github.com/alexcrichton"],"type":"OTHER"},{"name":"shumbo","contact":["https://github.com/shumbo"],"type":"OTHER"}]}