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CVE-2024-47763 — Wasmtime runtime crash when combining tail calls with trapping imports

2026-10-06T15:36:43.474293+00:00

Affected: bytecodealliance wasmtime

Wasmtime is an open source runtime for WebAssembly. Wasmtime's implementation of WebAssembly tail calls combined with stack traces can result in a runtime crash in certain WebAssembly modules. The runtime crash may be undefined behavior if Wasmtime was compiled with Rust 1.80 or prior. The runtime crash is a deterministic process abort when Wasmtime is compiled with Rust 1.81 and later. WebAssembly tail calls are a proposal which relatively recently reached stage 4 in the standardization process. Wasmtime first enabled support for tail calls by default in Wasmtime 21.0.0, although that release contained a bug where it was only on-by-default for some configurations. In Wasmtime 22.0.0 tail calls were enabled by default for all configurations. The specific crash happens when an exported function in a WebAssembly module (or component) performs a `return_call` (or `return_call_indirect` or `return_call_ref`) to an imported host function which captures a stack trace (for example, the host function raises a trap). In this situation, the stack-walking code previously assumed there was always at least one WebAssembly frame on the stack but with tail calls that is no longer true. With the tail-call proposal it's possible to have an entry trampoline appear as if it directly called the exit trampoline. This situation triggers an internal assert in the stack-walking code which raises a Rust `panic!()`. When Wasmtime is compiled with Rust versions 1.80 and prior this means that an `exter…

GHSA-q8hx-mm92-4wvg — wasmtime has a runtime crash when combining tail calls with trapping imports

2026-10-06T15:36:43.474365+00:00

Affected: crates.io: wasmtime

### Impact

Wasmtime's implementation of WebAssembly tail calls combined with stack traces can result in a runtime crash in certain WebAssembly modules. The runtime crash may be undefined behavior if Wasmtime was compiled with Rust 1.80 or prior. The runtime crash is a deterministic process abort when Wasmtime is compiled with Rust 1.81 and later.

[WebAssembly tail calls](https://github.com/webassembly/tail-call) are a proposal which relatively recently reached stage 4 in the [standardization process](https://github.com/WebAssembly/proposals/). Wasmtime first enabled support for tail calls by default [in Wasmtime 21.0.0](https://github.com/bytecodealliance/wasmtime/pull/8540), although that release contained a bug where it was only on-by-default for some configurations. In [Wasmtime 22.0.0](https://github.com/bytecodealliance/wasmtime/pull/8682) tail calls were enabled by default for all configurations.

The specific crash happens when an exported function in a WebAssembly module (or component) performs a `return_call` (or `return_call_indirect` or `return_call_ref`) to an imported host function which captures a stack trace (for example, the host function raises a trap). In this situation, the stack-walking code previously assumed there was always at least one WebAssembly frame on the stack but with tail calls that is no longer true. With the tail-call proposal it's possible to have an entry trampoline appear as if it directly called the exit trampoline. This situation trig…