CVE-2026-115391: Wasmtime 46.0.0 before 46.0.3 and 47.0.0 before 47.0.4 Unbounded Heap Allocation via WASIp3 Streams

Q: Which deployments are most exposed?

Deployments that run potentially malicious or untrusted WebAssembly guests and use WASIp3 file or HTTP write streams are exposed. The issue can exhaust host memory because guest-specified write lengths are buffered on the host.

Q: What does exploitation require?

A malicious guest must be able to submit very large buffers to WASIp3 file or HTTP write streams. The host then copies and buffers the supplied bytes, with the guest's linear memory as the stated bound.

Q: How can I determine whether an environment needs remediation?

Identify Wasmtime installations running 46.0.0 through 46.0.2 or 47.0.0 through 47.0.3, then determine whether they use the affected WASIp3 stream functionality. Update affected 46.x deployments to 46.0.3 or later and affected 47.x deployments to 47.0.4 or later.

Published Oct 22, 2026

Updated

Wasmtime 46.0.0 before 46.0.3 and 47.0.0 before 47.0.4 contains an uncontrolled resource allocation vulnerability in its WASIp3 implementation that buffers guest-specified-length writes on the host without limit. Malicious guests can offer large buffers to WASIp3 file or HTTP write streams, causing the host to copy and buffer all bytes, bounded only by guest linear memory, exhausting host memory.

Affected Software

1 affected component

Bytecode Alliance Wasmtime>=46.0.0<46.0.3, >=47.0.0<47.0.4

Event History

Oct 22, 2026

CVE Published

via MITRE·07:13 PM

Data Sourced

via MITRE·07:13 PM

DescriptionSeverityWeakness

Frequently Asked Questions

Which deployments are most exposed?

Deployments that run potentially malicious or untrusted WebAssembly guests and use WASIp3 file or HTTP write streams are exposed. The issue can exhaust host memory because guest-specified write lengths are buffered on the host.

What does exploitation require?

A malicious guest must be able to submit very large buffers to WASIp3 file or HTTP write streams. The host then copies and buffers the supplied bytes, with the guest's linear memory as the stated bound.

How can I determine whether an environment needs remediation?

Identify Wasmtime installations running 46.0.0 through 46.0.2 or 47.0.0 through 47.0.3, then determine whether they use the affected WASIp3 stream functionality. Update affected 46.x deployments to 46.0.3 or later and affected 47.x deployments to 47.0.4 or later.

CVE-2026-115391: Wasmtime 46.0.0 before 46.0.3 and 47.0.0 before 47.0.4 Unbounded Heap Allocation via WASIp3 Streams

Affected Software

Event History

Frequently Asked Questions

Which deployments are most exposed?

What does exploitation require?

How can I determine whether an environment needs remediation?

Company

Resources

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Frequently Asked Questions

Which deployments are most exposed?

What does exploitation require?

How can I determine whether an environment needs remediation?