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Medium, CVSS 4.1

Wasmtime segfault or unused out-of-sandbox load with f64.copysign operator on x86-64

CVE-2026-24116GHSA-vc8c-j3xm-xj73

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (wasmtime 41.0.1, 40.0.3, 36.0.5), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • crates.io wasmtime

    Affected
    >= 29.0.0, < 36.0.5>= 37.0.0, < 40.0.3>= 41.0.0, <= 41.0.0
    Fixed in
    41.0.1, 40.0.3, 36.0.5

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
4.1 · CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-24116: 0.25% estimated exploitation activity in the next 30 days; percentile 15.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

On x86-64 platforms with AVX Wasmtime's compilation of the f64.copysign WebAssembly instruction with Cranelift may load 8 more bytes than is necessary. When [signals-based-traps] are disabled this can result in a uncaught segfault due to loading from unmapped guard pages. With guard pages disabled it's possible for out-of-sandbox data to be loaded, but unless there is another bug in Cranelift this data is not visible to WebAssembly guests. Details The f64.copysign operator, when operating on a value loaded from a memory (for example with f64.load), compiles with Cranelift to code on x86-64 with AVX that loads 128 bits (16 bytes) rather than the expected 64 bits (8 bytes) from memory. When the address is in-bounds for a (correct) 8-byte load but not an (incorrect) 16-byte load, this can load beyond memory by up to 8 bytes. This can result in three different behaviors depending on Wasmtime's configuration: 1. If guard pages are disabled then this extra data will be loaded. The extra…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-vc8c-j3xm-xj73

Agent brief

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# Patch Next advisory brief: CVE-2026-24116

Advisory: Wasmtime segfault or unused out-of-sandbox load with f64.copysign operator on x86-64
IDs: CVE-2026-24116, GHSA-vc8c-j3xm-xj73
Record: https://patchnext.com/advisories/cve-2026-24116 (revision 1, source checked 26 Oct 2026, 15:39 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: wasmtime 41.0.1, 40.0.3, 36.0.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io wasmtime: affected >= 29.0.0, < 36.0.5; >= 37.0.0, < 40.0.3; >= 41.0.0, <= 41.0.0; fixed in 41.0.1, 40.0.3, 36.0.5

## Suggested inspection (read-only)
- crates.io wasmtime: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on wasmtime.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-vc8c-j3xm-xj73 (GitHub-reviewed advisory GHSA-vc8c-j3xm-xj73 lists affected ranges: crates.io wasmtime >=29.0.0 =37.0.0 =41.0.0 <=41.0.0)

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