Wasmtime component start function panic

Severity: medium · CVSS 4 · Published 2026-10-14

Wasmtime is a WebAssembly runtime used to execute WebAssembly components. A flaw in how component start functions handle certain operations can cause the host process to panic and crash, disrupting any service relying on it.

Technologies: Bytecode Alliance Wasmtime, wasmtime (crates.io). Vendors: Bytecode Alliance, crates.io.

Quick answers

Is This vulnerability exploited in the wild?
No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
How severe is This vulnerability?
Medium severity, with a CVSS score of 4, published 14 October 2026.
Which products and versions are affected?
Bytecode Alliance Wasmtime 46.0.0 to 48.0.5, 49.0.0 to 49.0.2; wasmtime (crates.io) SEMVER:introduced=46.0.0,fixed=48.0.6,introduced=49.0.0,fixed=49.0.3.
Is there a fix for This vulnerability?
Yes. wasmtime (crates.io): upgrade to 49.0.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is This vulnerability attacked?
It is attacked over the network.
Am I affected?
Check whether you run Bytecode Alliance Wasmtime or wasmtime (crates.io) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • wasmtime (crates.io): upgrade to 49.0.3 or later
    cargo update -p wasmtime

Technical details

A yield operation in a component start function can trigger a host panic in Wasmtime's component model implementation. The vulnerability requires network access, low privileges, user interaction, and specific attack prerequisites. Successful exploitation results in denial of service via host process termination.

Affected products

  • Bytecode Alliance Wasmtime 46.0.0 to 48.0.5, 49.0.0 to 49.0.2

Identifiers

  • GHSA-5hhx-4wrr-3j9g
  • RUSTSEC-2026-0358

Timeline

  • 2026-10-14: disclosed

References

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