CVE-2023-27477 is a low-severity (CVSS 3.1) CWE-193 vulnerability in wasmtime. A fix is available for wasmtime — see the affected versions and patch details below.
wasmtime vulnerable to miscompilation of `i8x16.select` with the same inputs on x86_64
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-27477.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
wasmtime🦀wasmtime🦀wasmtime🦀cranelift-codegen🦀cranelift-codegen🦀cranelift-codegenReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
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
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
- Mailing list announcement
- GitHub advisory
- Commit to fix this issue on Wasmtime's
mainbranch
For more information
If you have any questions or comments about this advisory:
- Reach out to us on the Bytecode Alliance Zulip chat
- Open an issue in the bytecodealliance/wasmtime repository
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | wasmtime | ≥ 1.0.0&&< 4.0.1 | 4.0.1cargo update -p wasmtime --precise 4.0.1 |
| 🦀crates.io | wasmtime | ≥ 5.0.0&&< 5.0.1 | 5.0.1cargo update -p wasmtime --precise 5.0.1 |
| 🦀crates.io | wasmtime | ≥ 6.0.0&&< 6.0.1 | 6.0.1cargo update -p wasmtime --precise 6.0.1 |
| 🦀crates.io | cranelift-codegen | ≥ 0.88.0&&< 0.91.1 | 0.91.1cargo update -p cranelift-codegen --precise 0.91.1 |
| 🦀crates.io | cranelift-codegen | ≥ 0.92.0&&< 0.92.1 | 0.92.1cargo update -p cranelift-codegen --precise 0.92.1 |
| 🦀crates.io | cranelift-codegen | ≥ 0.93.0&&< 0.93.1 | 0.93.1cargo update -p cranelift-codegen --precise 0.93.1 |
Affected Products
cranelift-codegenbytecodealliancewasmtimebytecodeallianceDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for wasmtime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update wasmtime to 4.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-27477 is resolved across your whole dependency graph.
Workarounds
Close the privilege gap rather than the entry point: audit which accounts, roles and service identities can reach the affected operation, drop the component to the least privilege it actually needs, and review file and directory permissions created by earlier installs — a default left in place is what makes this reachable.
Frequently Asked Questions
Is CVE-2023-27477 in your dependencies?
Find it across crates.io, including transitive dependencies.