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Low, CVSS 2.0amended

Wasmtime: Preemption and traps during bulk operations enable breaking internal VM state

CVE-2026-104855GHSA-2hw9-mc66-jc2q

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (wasmtime 47.0.3, 46.0.2), 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
    >= 46.0.0, < 46.0.2>= 47.0.0, < 47.0.3
    Fixed in
    47.0.3, 46.0.2

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
2.0 · CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:P/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2026-104855: 0.28% estimated exploitation activity in the next 30 days; percentile 20.12 (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.

Impact Wasmtime's implementation of bulk-data-transfer WebAssembly instructions, such as memory.copy, contains a vulnerability when a preemption via epochs or fuel is combined with altering the store's state or cancelling a computation. To prevent these operations from taking too long Wasmtime injects fuel/epoch checks during these operations, but this enables embedders, and possible WebAssembly, to witness intermediate state in the middle of the operation. Examples of this include: When a non-nullable WebAssembly table is grown the new elements initially start as null and are filled in as part of a loop with preemption checks. If this computation is then cancelled this left the table in a grown-but-uninitialized state where subsequent usage via WebAssembly could possibly segfault. Loads from this table are assumed to not be null due to its type, but the runtime implementation was exposed through this cancellation at a preemption point. Embedders could mutate the store during an…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-2hw9-mc66-jc2q

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record RUSTSEC-2026-0223

  4. Revision 1 · created ·

    Published from osv record GHSA-2hw9-mc66-jc2q

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-104855

Advisory: Wasmtime: Preemption and traps during bulk operations enable breaking internal VM state
IDs: CVE-2026-104855, GHSA-2hw9-mc66-jc2q
Record: https://patchnext.com/advisories/cve-2026-104855 (revision 4, source checked 26 Oct 2026, 15:43 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.0)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: wasmtime 47.0.3, 46.0.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io wasmtime: affected >= 46.0.0, < 46.0.2; >= 47.0.0, < 47.0.3; fixed in 47.0.3, 46.0.2

## 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://osv.dev/vulnerability/GHSA-2hw9-mc66-jc2q (OSV record GHSA-2hw9-mc66-jc2q lists affected ranges: crates.io wasmtime >=46.0.0 =47.0.0 <47.0.3 (fixed))
- Verified: https://osv.dev/vulnerability/RUSTSEC-2026-0223 (OSV record RUSTSEC-2026-0223 lists affected ranges: crates.io wasmtime >=46.0.0 =47.0.0 <47.0.3 (fixed))
- Verified: https://github.com/advisories/GHSA-2hw9-mc66-jc2q (GitHub-reviewed advisory GHSA-2hw9-mc66-jc2q lists affected ranges: crates.io wasmtime >=46.0.0 =47.0.0 <47.0.3)

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