CVE-2026-104855
Deferred Deferred - Pending Action

Memory Corruption in Wasmtime Due to Bulk Operation Checks

Publication date: 2026-10-02

Last updated on: 2026-10-02

Assigner: GitHub, Inc.

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.

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Meta Information

Published
2026-10-02
Last Modified
2026-10-02
Generated
2026-10-02
AI Q&A
2026-10-02
EPSS Evaluated
N/A
NVD
CVE-2026-104855
EUVD
EUVD-2026-91765

Affected Vendors & Products

Showing 10 associated CPEs
Vendor Product Version / Range
wasmtime wasmtime From 46.0.0 (inc) to 46.0.3 (exc)
wasmtime wasmtime 47.0.3
wasmtime wasmtime 46.0.2
bytecodealliance wasmtime From 46.0.0 (inc) to 46.0.3 (exc)
bytecodealliance wasmtime From 46.0.1 (inc) to 46.0.3 (exc)
bytecodealliance wasmtime From 47.0.0 (inc) to 47.0.3 (exc)
bytecodealliance wasmtime From 47.0.1 (inc) to 47.0.3 (exc)
bytecodealliance wasmtime From 47.0.2 (inc) to 47.0.3 (exc)
bytecodealliance wasmtime 46.0.2
bytecodealliance wasmtime 47.0.3

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-362 The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

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Executive Summary

CVE-2026-104855 is a vulnerability in Wasmtime, a WebAssembly runtime, affecting versions 46.0.0 to 47.0.2. It occurs when preemption (via epochs or fuel) interacts with bulk operations like memory.copy, table.grow, or array.copy. These operations expose internal VM state during preemption points, allowing embedders to manipulate intermediate states. This can lead to crashes, invalid memory access, or heap corruption. The issue is fixed in versions 46.0.2 and 47.0.3.

Detection Guidance

Detecting this vulnerability requires checking the installed Wasmtime version. Run: wasmtime --version. If the version is between 46.0.0-46.0.1 or 47.0.0-47.0.2, the system is vulnerable.

Impact Analysis

This vulnerability can cause crashes, invalid memory access, or heap corruption in applications using affected Wasmtime versions. It requires specific embedding patterns, such as using Store::epoch_deadline_callback or mutating the store after timeouts. Exploitation is difficult as it needs high privileges and precise conditions. Workarounds include avoiding store mutations in epoch callbacks or discarding the store after trapping.

Compliance Impact

This vulnerability does not directly impact compliance with GDPR, HIPAA, or similar standards. The issue is specific to Wasmtime's internal VM state corruption during bulk operations and preemption, which could lead to crashes or memory corruption. There is no evidence in the provided context that this vulnerability exposes or leaks sensitive data, which is a primary concern for GDPR and HIPAA compliance.

Mitigation Strategies

Upgrade Wasmtime to version 46.0.2 or 47.0.3 or later. Avoid using Store mutations in epoch callbacks or resuming Wasm after trapping. Discard Stores after timeouts or epoch deadlines.

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