# CVE-2026-104855: Wasmtime: Preemption and traps during bulk operations enable breaking internal VM state

> Attackers can trigger memory corruption or crashes in Wasmtime by exploiting race conditions during preemption in bulk operations, requiring specific embedder configurations.

- **Severity:** Low 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`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 2 Oct 2026
- **Updated:** 6 Oct 2026
- **Also known as:** GHSA-2hw9-mc66-jc2q, MINI-8q69-px44-24m3, MINI-gw92-qq7c-qm3x, MINI-rh88-59v6-8775, RUSTSEC-2026-0223, UBUNTU-CVE-2026-104855

## What is CVE-2026-104855?

CVE-2026-104855 is a low-severity vulnerability in bytecodealliance wasmtime, published on 2 Oct 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

### Official description

Wasmtime is a runtime for WebAssembly. From 46.0.0 until 46.0.2 and 47.0.3, fuel and epoch preemption checks inside bulk operations including memory.copy, table.grow, and array.copy can expose invalid intermediate state when an embedder mutates a Store in Store::epoch_deadline_callback or continues using a Store after cancellation or a trap. A cancelled non-nullable table growth can leave null elements, linear-memory growth during memory.copy can invalidate retained raw pointers, and callback-triggered garbage collection during array.copy can invalidate GC pointers, resulting in a crash, invalid memory access, or GC heap corruption. Embeddings whose callbacks only access the host data in Store<T>, and embeddings that discard a Store after timeout or epoch deadline, are not affected. This issue is fixed in versions 46.0.2 and 47.0.3.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-104855?

5 open source packages ship an affected version, including wasmtime.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `wasmtime` | crates.io | From 46.0.0 | 46.0.2, 47.0.3 |
| `wasmtime` | crates.io | From 46.0.0 | 46.0.2 |
| `wasmtime` | crates.io | From 46.0.0 | 46.0.2 |
| `wasmtime` | crates.io | From 47.0.0 | 47.0.3 |
| `wasmtime` | crates.io | From 47.0.0 | 47.0.3 |

## How do I fix CVE-2026-104855?

Upgrade wasmtime to a fixed version for your release line: 46.0.2 or 47.0.3.

## Is CVE-2026-104855 being exploited?

There is no known exploitation of CVE-2026-104855 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-104855 and fix it if it is affected.

What it is: CVE-2026-104855 is a low-severity vulnerability in bytecodealliance wasmtime, published on 2 Oct 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-104855 in the wild and no public exploit code.

Affected packages and fixed versions:
- wasmtime (crates.io): affected from 46.0.0; fixed in 46.0.2, 47.0.3
- wasmtime (crates.io): affected from 46.0.0; fixed in 46.0.2
- wasmtime (crates.io): affected from 46.0.0; fixed in 46.0.2
- wasmtime (crates.io): affected from 47.0.0; fixed in 47.0.3
- wasmtime (crates.io): affected from 47.0.0; fixed in 47.0.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-104855/ (Markdown: https://insights.sbomify.com/CVE-2026-104855/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-104855
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-104855
- OSV: https://osv.dev/vulnerability/CVE-2026-104855

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-104855/
Summaries are generated and may contain mistakes; the official description above is the record.