CVE-2026-27572
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Denial of Service via Header Overflow in Wasmtime wasi:http

Publication date: 2026-02-24

Last updated on: 2026-02-25

Assigner: GitHub, Inc.

Description
Wasmtime is a runtime for WebAssembly. Prior to versions 24.0.6, 36.0.6, 4.0.04, 41.0.4, and 42.0.0, Wasmtime's implementation of the `wasi:http/types.fields` resource is susceptible to panics when too many fields are added to the set of headers. Wasmtime's implementation in the `wasmtime-wasi-http` crate is backed by a data structure which panics when it reaches excessive capacity and this condition was not handled gracefully in Wasmtime. Panicking in a WASI implementation is a Denial of Service vector for embedders and is treated as a security vulnerability in Wasmtime. Wasmtime 24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0 patch this vulnerability and return a trap to the guest instead of panicking. There are no known workarounds at this time. Embedders are encouraged to update to a patched version of Wasmtime.
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Meta Information
Published
2026-02-24
Last Modified
2026-02-25
Generated
2026-06-16
AI Q&A
2026-02-25
EPSS Evaluated
2026-06-15
NVD
CVE-2026-27572
EUVD
EUVD-2026-8569
Affected Vendors & Products
Showing 4 associated CPEs
Vendor Product Version / Range
bytecodealliance wasmtime to 24.0.6 (exc)
bytecodealliance wasmtime From 25.0.0 (inc) to 36.0.6 (exc)
bytecodealliance wasmtime From 37.0.0 (inc) to 40.0.4 (exc)
bytecodealliance wasmtime From 41.0.0 (inc) to 41.0.4 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-770 The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
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Executive Summary

This vulnerability affects Wasmtime, a runtime for WebAssembly, specifically in its implementation of the `wasi:http/types.fields` resource. When too many header fields are added, the underlying data structure in the `wasmtime-wasi-http` crate panics due to excessive capacity. This panic is not handled gracefully, causing the runtime to crash. Such panics in a WASI implementation can lead to a Denial of Service (DoS) condition for applications embedding Wasmtime.

The issue is fixed in Wasmtime versions 24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0, where the runtime returns a trap to the guest instead of panicking. There are currently no known workarounds, so users are encouraged to update to a patched version.

Impact Analysis

This vulnerability can cause Wasmtime to panic and crash when processing too many HTTP header fields, leading to a Denial of Service (DoS) for applications that rely on Wasmtime for WebAssembly execution. This means that an attacker could potentially disrupt the availability of services or applications embedding Wasmtime by triggering this condition.

Compliance Impact

I don't know

Detection Guidance

I don't know

Mitigation Strategies

To mitigate this vulnerability, you should update Wasmtime to one of the patched versions: 24.0.6, 36.0.6, 40.0.4, 41.0.4, or 42.0.0.

There are no known workarounds at this time, so upgrading to a fixed version is the recommended immediate action.

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