CVE-2025-61670: Wasmtime is a runtime for WebAssembly. (CVSS 1)

Wasmtime is a runtime for WebAssembly.

Wasmtime is a runtime for WebAssembly. Wasmtime 37.0.0 and 37.0.1 have memory leaks in the C/C++ API when using bindings for the `anyref` or `externref` WebAssembly values. This is caused by a regression introduced during the development of 37.0.0 and all prior versions of Wasmtime are unaffected. If `anyref` or `externref` is not used in the C/C++ API then embeddings are also unaffected by the leaky behavior. The `wasmtime` Rust crate is unaffected by this leak. Development of Wasmtime 37.0.0 included a refactoring in Rust of changing the old `ManuallyRooted<T>` type to a new `OwnedRooted<T>` type. This change was integrated into Wasmtime's C API but left the C API in a state which had memory leaks. Additionally the new ownership semantics around this type were not reflected into the C++ API, making it leak-prone. A short version of the change is that previously `ManuallyRooted<T>`, as the name implies, required manual calls to an "unroot" operation. If this was forgotten then the memory was still cleaned up when the `wasmtime_store_t` itself was destroyed eventually. Documentation of when to "unroot" was sparse and there were already situations prior to 37.0.0 where memory would

Description from the National Vulnerability Database, published by GitHub

What it means for a small business

If your business uses wasmtime, install the vendor's update. If you're not sure whether you use it, ask whoever manages your computers.

How likely is an attack? The Exploit Prediction Scoring System, run by FIRST (the global association of security response teams), puts the odds of this one being exploited in the next 30 days at 0.19%, higher than 9% of CVEs. That’s low, but low isn’t zero, and the odds jump the day someone publishes an exploit. Scored October 28, 2026, updated daily.

Check your own setup

Website check: reads what your site runs from the outside (WordPress version, plugins it can see, old server software) and matches it against this database.
Server check: what your web server says about itself, and whether that version has known flaws.

Sources

Part of the Huttenlocher Technologies vulnerability database, refreshed twice a day from CISA and the NVD. The title, category and plain-language guidance are ours; check the linked record before acting on a detail. This is general guidance, not a review of your systems.

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