{"id":"GHSA-q879-9g95-56mx","summary":"Wrong type for `Linker`-define functions when used across two `Engine`s","details":"### Impact\n\nAs a Rust library the `wasmtime` crate clearly marks which functions are safe and which are `unsafe`, guaranteeing that if consumers never use `unsafe` then it should not be possible to have memory unsafety issues in their embeddings of Wasmtime. An issue was discovered in the safe API of `Linker::func_*` APIs. These APIs were previously not sound when one `Engine` was used to create the `Linker` and then a different `Engine` was used to create a `Store` and then the `Linker` was used to instantiate a module into that `Store`. Cross-`Engine` usage of functions is not supported in Wasmtime and this can result in type confusion of function pointers, resulting in being able to safely call a function with the wrong type.\n\nTriggering this bug requires using at least two `Engine` values in an embedding and then additionally using two different values with a `Linker` (one at the creation time of the `Linker` and another when instantiating a module with the `Linker`).\n\nIt's expected that usage of more-than-one `Engine` in an embedding is relatively rare since an `Engine` is intended to be a globally shared resource, so the expectation is that the impact of this issue is relatively small.\n\nThe fix implemented is to change this behavior to `panic!()` in Rust instead of silently allowing it. Using different `Engine` instances with a `Linker` is a programmer bug that `wasmtime` catches at runtime.\n\n### Patches\n\nThis bug has been patched and users should upgrade to Wasmtime version 0.30.0.\n\n### Workarounds\n\nIf you cannot upgrade Wasmtime and are using more than one `Engine` in your embedding it's recommended to instead use only one `Engine` for the entire program if possible. An `Engine` is designed to be a globally shared resource that is suitable to have only one for the lifetime of an entire process. If using multiple `Engine`s is required then code should be audited to ensure that `Linker` is only used with one `Engine`.\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n\n* Reach out to us on [the Bytecode Alliance Zulip chat](https://bytecodealliance.zulipchat.com/#narrow/stream/217126-wasmtime)\n* Open an issue in [the `bytecodealliance/wasmtime` repository](https://github.com/bytecodealliance/wasmtime/)","aliases":["CVE-2021-39216","CVE-2021-39218","CVE-2021-39219","GHSA-4873-36h9-wv49","GHSA-v4cp-h94r-m7xf","PYSEC-2021-320","PYSEC-2021-321","PYSEC-2021-322","RUSTSEC-2021-0110"],"modified":"2026-05-15T12:14:12.792168682Z","published":"2021-09-20T19:54:26Z","database_specific":{"cwe_ids":["CWE-843"],"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2021-09-17T20:07:13Z","nvd_published_at":"2021-09-17T20:15:00Z"},"references":[{"type":"WEB","url":"https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-q879-9g95-56mx"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-39219"},{"type":"WEB","url":"https://github.com/bytecodealliance/wasmtime/commit/b39f087414f27ae40c44449ed5d1154e03449bff"},{"type":"WEB","url":"https://crates.io/crates/wasmtime"},{"type":"PACKAGE","url":"https://github.com/bytecodealliance/wasmtime"},{"type":"WEB","url":"https://github.com/bytecodealliance/wasmtime-py/compare/0.29.0...0.30.0"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/wasmtime/PYSEC-2021-322.yaml"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WAVBRYDDUIY2ZR3K3FO4BVYJKIMJ5TP7"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/Z2Z33FTXFQ6EOINVEQIP4DFBG53G5XIY"},{"type":"WEB","url":"https://rustsec.org/advisories/RUSTSEC-2021-0110.html"}],"affected":[{"package":{"name":"wasmtime","ecosystem":"crates.io","purl":"pkg:cargo/wasmtime"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.30.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/09/GHSA-q879-9g95-56mx/GHSA-q879-9g95-56mx.json"}},{"package":{"name":"wasmtime","ecosystem":"PyPI","purl":"pkg:pypi/wasmtime"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.30.0"}]}],"versions":["0.0.1","0.0.2","0.11.0","0.12.0","0.15.0","0.15.1","0.16.0","0.16.1","0.17.0","0.18.0","0.18.1","0.18.2","0.19.0","0.20.0","0.21.0","0.22.0","0.23.0","0.24.0","0.25.0","0.26.0","0.27.0","0.28.0","0.28.1","0.29.0","0.9.0"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/09/GHSA-q879-9g95-56mx/GHSA-q879-9g95-56mx.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N"}]}