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GHSA-xm67-587q-r2vw CVE-2023-27477 RUSTSEC-2023-0093

wasmtime vulnerable to miscompilation of `i8x16.select` with the same inputs on x86_64

Medium crates.io
Severity
3.1 / 10
Medium · CVSS 3.1
Exploit chance (EPSS)
0.62%
Chance of exploitation in the next 30 days. Higher than 49.93% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-193 Off-by-one Error
Fix
Available
2 packages have a fixed version

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

For more information

If you have any questions or comments about this advisory:

Affected versions

crates.io

PackageVulnerableFixed in
cranelift-codegen
>= 0.88.0, < 0.91.1
0.91.1
cranelift-codegen
>= 0.92.0, < 0.92.1
0.92.1
cranelift-codegen
>= 0.93.0, < 0.93.1
0.93.1
wasmtime
>= 1.0.0, < 4.0.1
4.0.1
wasmtime
>= 5.0.0, < 5.0.1
5.0.1
wasmtime
>= 6.0.0, < 6.0.1
6.0.1
wasmtime
>= 0.0.0-0, < 4.0.1
>= 5.0.0, < 5.0.1
>= 6.0.0, < 6.0.1
4.0.1
5.0.1
6.0.1

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

cranelift-codegen crates.io → 0.91.1

cargo
cargo update -p cranelift-codegen --precise 0.91.1

wasmtime crates.io → 4.0.1

cargo
cargo update -p wasmtime --precise 4.0.1

Severity breakdown

CVSS 3.1 3.1

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

Attack vector
Network
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

Weakness

CWE-193: Off-by-one Error

A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.

How to prevent it
  • Implementation: When copying character arrays or using character manipulation methods, the correct size parameter must be used to account for the null terminator that needs to be added at the end of the array. Some examples of functions susceptible to this weakness in C include strcpy(), strncpy(), strcat(), strncat(), printf(), sprintf(), scanf() and sscanf().

References

Advisories

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
RUSTSEC-2026-0424
Unchecked memory usage in transferring borrowed resources between components
Not rated yet Also affects wasmtime
RUSTSEC-2026-0423
Cross-engine type confusion with host-created struct-types-with-supertypes
Not rated yet Also affects wasmtime
RUSTSEC-2026-0422
Typed functions with `i31` or `nullref` arguments may panic due to insufficient type-check
Low Also affects wasmtime
RUSTSEC-2026-0379
Wasmtime: Cranelift backend on aarch64 can jump to incorrect target on large Wasm `br_table` instruction
Critical Also affects wasmtime
GHSA-9pvw-hwfg-92h5
Wasmtime: Panic lowering a host-created component model stream into a guest that expects a different payload type
Medium Also affects wasmtime
GHSA-897f-g5gm-fmxm
Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation
Critical Also affects wasmtime
RUSTSEC-2026-0364
Exception tags can cause host data structures to be unaligned
Not rated yet Also affects wasmtime
RUSTSEC-2026-0363
Component-model handle tables are capped only per instance and charged to no limit
Medium Also affects wasmtime
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