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.
- 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
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
Which versions are affected by CVE-2026-104855?
5 open source packages ship an affected version, including wasmtime.
| Package | 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.
Sources
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.