CVE-2022-31104: Wasmtime is a standalone runtime for WebAssembly. In affected versions wasmtime's implementation of the SIMD proposal for WebAssembly on x86_64 contai...

Description

Wasmtime is a standalone runtime for WebAssembly. In affected versions wasmtime's implementation of the SIMD proposal for WebAssembly on x86_64 contained two distinct bugs in the instruction lowerings implemented in Cranelift. The aarch64 implementation of the simd proposal is not affected. The bugs were presented in the `i8x16.swizzle` and `select` WebAssembly instructions. The `select` instruction is only affected when the inputs are of `v128` type. The correspondingly affected Cranelift instructions were `swizzle` and `select`. The `swizzle` instruction lowering in Cranelift erroneously overwrote the mask input register which could corrupt a constant value, for example. This means that future uses of the same constant may see a different value than the constant itself. The `select` instruction lowering in Cranelift wasn't correctly implemented for vector types that are 128-bits wide. When the condition was 0 the wrong instruction was used to move the correct input to the output of the instruction meaning that only the low 32 bits were moved and the upper 96 bits of the result were left as whatever the register previously contained (instead of the input being moved from). The `select` instruction worked correctly if the condition was nonzero, however. This bug in Wasmtime's implementation of these instructions on x86_64 represents an incorrect implementation of the specified semantics of these instructions according to the WebAssembly specification. The impact of this is benign for hosts running WebAssembly but represents possible vulnerabilities within the execution of a guest program. For example a WebAssembly program could take unintended branches or materialize incorrect values internally which runs the risk of exposing the program itself to other related vulnerabilities which can occur from miscompilations. We have released Wasmtime 0.38.1 and cranelift-codegen (and other associated cranelift crates) 0.85.1 which contain the corrected implementations of these two instructions in Cranelift. If upgrading is not an option for you at this time, you can avoid the vulnerability by disabling the Wasm simd proposal. Additionally the bug is only present on x86_64 hosts. Other aarch64 hosts are not affected. Note that s390x hosts don't yet implement the simd proposal and are not affected.

Metrics

CVSS 3.1

5.6/10

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

EPSS Probability

1.63%

73.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-682

Affected Software

Vendor	Product	Versions
Bytecodealliance	Cranelift-Codegen	< 0.85.0
Bytecodealliance	Wasmtime	< 0.38.1

References

https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.wasm_simdThird Party Advisory
https://github.com/bytecodealliance/wasmtime/pull/4317Issue Tracking, Patch, Third Party Advisory
https://github.com/bytecodealliance/wasmtime/pull/4318Issue Tracking, Patch, Third Party Advisory
https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-jqwc-c49r-4w2xMitigation, Third Party Advisory
https://github.com/webassembly/simdThird Party Advisory
https://webassembly.github.io/spec/Third Party Advisory
https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.wasm_simdThird Party Advisory
https://github.com/bytecodealliance/wasmtime/pull/4317Issue Tracking, Patch, Third Party Advisory
https://github.com/bytecodealliance/wasmtime/pull/4318Issue Tracking, Patch, Third Party Advisory
https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-jqwc-c49r-4w2xMitigation, Third Party Advisory
https://github.com/webassembly/simdThird Party Advisory
https://webassembly.github.io/spec/Third Party Advisory

Timeline

Published: Jun 28, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2022-31104?

Wasmtime is a standalone runtime for WebAssembly. In affected versions wasmtime's implementation of the SIMD proposal for WebAssembly on x86_64 contained two distinct bugs in the instruction lowerings implemented in Cranelift. The aarch64 implementation of the simd proposal is not affected. The bugs were presented in the `i8x16.swizzle` and `select` WebAssembly instructions. The `select` instruction is only affected when the inputs are of `v128` type. The correspondingly affected Cranelift instructions were `swizzle` and `select`. The `swizzle` instruction lowering in Cranelift erroneously overwrote the mask input register which could corrupt a constant value, for example. This means that future uses of the same constant may see a different value than the constant itself. The `select` instruction lowering in Cranelift wasn't correctly implemented for vector types that are 128-bits wide. When the condition was 0 the wrong instruction was used to move the correct input to the output of the instruction meaning that only the low 32 bits were moved and the upper 96 bits of the result were left as whatever the register previously contained (instead of the input being moved from). The `select` instruction worked correctly if the condition was nonzero, however. This bug in Wasmtime's implementation of these instructions on x86_64 represents an incorrect implementation of the specified semantics of these instructions according to the WebAssembly specification. The impact of this is benign for hosts running WebAssembly but represents possible vulnerabilities within the execution of a guest program. For example a WebAssembly program could take unintended branches or materialize incorrect values internally which runs the risk of exposing the program itself to other related vulnerabilities which can occur from miscompilations. We have released Wasmtime 0.38.1 and cranelift-codegen (and other associated cranelift crates) 0.85.1 which contain the corrected implementations of these two instructions in Cranelift. If upgrading is not an option for you at this time, you can avoid the vulnerability by disabling the Wasm simd proposal. Additionally the bug is only present on x86_64 hosts. Other aarch64 hosts are not affected. Note that s390x hosts don't yet implement the simd proposal and are not affected.

How severe is CVE-2022-31104?

CVE-2022-31104 has a CVSS score of 5.6/10 (MEDIUM severity). The EPSS model estimates a 1.63% probability of exploitation in the next 30 days.

How do I fix CVE-2022-31104?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.