wasmtime is a fast and secure runtime for WebAssembly. Wasmtime's code generation backend, Cranelift, has a bug on x86_64 platforms for the WebAssembly `i8x16.select` instruction which will produce the wrong results when the same operand is…

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wasmtime is a fast and secure runtime for WebAssembly. Wasmtime's code generation backend, Cranelift, has a bug on x86_64 platforms for the WebAssembly `i8x16.select` instruction which will produce the wrong results when the same operand is provided to the instruction and some of the selected indices are greater than 16. There is an off-by-one error in the calculation of the mask to the `pshufb` instruction which causes incorrect results to be returned if lanes are selected from the second vector. This codegen bug has been fixed in Wasmtiem 6.0.1, 5.0.1, and 4.0.1. Users are recommended to upgrade to these updated versions. If upgrading is not an option for you at this time, you can avoid this miscompilation by disabling the Wasm simd proposal. Additionally the bug is only present on x86_64 hosts. Other platforms such as AArch64 and s390x are not affected.

Source published

8 Mar 2023 00:00:00 UTC

Source modified

25 Feb 2025 14:59:59 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N

wasmtime is a fast and secure runtime for WebAssembly. Wasmtime's code generation backend, Cranelift, has a bug on x86_64 platforms for the WebAssembly `i8x16.select` instruction which will produce the wrong results when the same operand is provided to the instruction and some of the selected indices are greater than 16. There is an off-by-one error in the calculation of the mask to the `pshufb` instruction which causes incorrect results to be returned if lanes are selected from the second vector. This codegen bug has been fixed in Wasmtiem 6.0.1, 5.0.1, and 4.0.1. Users are recommended to upgrade to these updated versions. If upgrading is not an option for you at this time, you can avoid this miscompilation by disabling the Wasm simd proposal. Additionally the bug is only present on x86_64 hosts. Other platforms such as AArch64 and s390x are not affected.

Source published

Mar 8, 2023, 12:00:00 AM (timezone not stated)

Source modified

Feb 25, 2025, 2:59:59 PM (timezone not stated)

Observed here

10 Nov 2026 01:22:39 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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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 3.1 · 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N

wasmtime is a fast and secure runtime for WebAssembly. Wasmtime's code generation backend, Cranelift, has a bug on x86_64 platforms for the WebAssembly `i8x16.select` instruction which will produce the wrong results when the same operand is provided to the instruction and some of the selected indices are greater than 16. There is an off-by-one error in the calculation of the mask to the `pshufb` instruction which causes incorrect results to be returned if lanes are selected from the second vector. This codegen bug has been fixed in Wasmtiem 6.0.1, 5.0.1, and 4.0.1. Users are recommended to upgrade to these updated versions. If upgrading is not an option for you at this time, you can avoid this miscompilation by disabling the Wasm simd proposal. Additionally the bug is only present on x86_64 hosts. Other platforms such as AArch64 and s390x are not affected.

Source published

8 Mar 2023 21:15:11 UTC

Source modified

17 Jun 2026 05:45:17 UTC

Observed here

24 Oct 2026 21:17:34 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 3.1 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N

CVSS 3.1 · [email protected] · Primary · 4.3 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

### Impact Wasmtime's code generation backend, Cranelift, has a bug on x86_64 platforms for the WebAssembly `i8x16.select` instruction which will produce the wrong results when the same operand is provided to the instruction and some of the selected indices are greater than 16. There is an off-by-one error in the calculation of the mask to the `pshufb` instruction which causes incorrect results to be returned if lanes are selected from the second vector. The impact of this miscompilation is that the WebAssembly instruction can produce incorrect results for the `i8x16.select` instruction. This should have no effect on embedders and does not represent a sandbox escape, for example. Guest programs, however, may behave unexpectedly due to the incorrect result of this instruction. In extreme cases if a guest program is handling untrusted input then the guest program may deviate from its intended execution, for example calling an imported host function with different arguments than intended. This still does not impact embedders, however, because there is no form of privilege escalation with the guest. At this time it's expected that this codegen pattern doesn't show up in the wild that often. LLVM-generated modules, for example, do not appear to conventionally or idiomatically generate code which would hit this bug. It is possible, however, to still write code which triggers this, so it's recommended for embedders to analyze existing modules to see if any are affected. ### Patches This codegen bug has been fixed in Wasmtime 6.0.1, 5.0.1, and 4.0.1. Users are recommended to upgrade to these updated versions. ### Workarounds If upgrading is not an option for you at this time, you can avoid this miscompilation by [disabling the Wasm simd proposal](https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.wasm_simd) ```rust config.wasm_simd(false); ``` Additionally the bug is only present on x86_64 hosts. Other platforms such as AArch64 and s390x are not affected. ### References * [The WebAssembly simd proposal](https://github.com/webassembly/simd) * [Mailing list announcement](https://groups.google.com/a/bytecodealliance.org/g/sec-announce/c/Mov-ItrNJsQ) * [GitHub advisory](https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-xm67-587q-r2vw) * [Commit to fix this issue on Wasmtime's `main` branch](https://github.com/bytecodealliance/wasmtime/commit/5dc2bbccbb363e474d2c9a1b8e38a89a43bbd5d1) ### For more information If you have any questions or comments about this advisory: * Reach out to us on [the Bytecode Alliance Zulip chat](https://bytecodealliance.zulipchat.com/#narrow/stream/217126-wasmtime) * Open an issue in [the bytecodealliance/wasmtime repository](https://github.com/bytecodealliance/wasmtime/)

Source published

9 Mar 2023 00:09:03 UTC

Source modified

10 Sep 2026 03:49:53 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N

Publisher rating · LOW

This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-xm67-587q-r2vw. For more information see the GitHub-hosted security advisory.

Source published

3 Mar 2023 12:00:00 UTC

Source modified

12 Oct 2026 18:00:06 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

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: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N