CVE-2025-53901: Wasmtime CLI is vulnerable to host panic through its fd_renumber function

A bug in Wasmtime’s implementation of the WASIp1 set of import functions can lead to a WebAssembly guest inducing a panic in the host (embedder). The specific bug is triggered by calling path_open after calling fd_renumber with either:

• two equal argument values
• second argument being equal to a previously-closed file descriptor number value

The corrupt state introduced in fd_renumber will lead to the subsequent opening of a file descriptor to panic. This panic cannot introduce memory unsafety or allow WebAssembly to break outside of its sandbox, however. There is no possible heap corruption or memory unsafety from this panic.

This bug is in the implementation of Wasmtime’s wasmtime-wasi crate which provides an implementation of WASIp1. The bug requires a specially crafted call to fd_renumber in addition to the ability to open a subsequent file descriptor. Opening a second file descriptor is only possible when a preopened directory was provided to the guest, and this is common amongst embeddings. A panic in the host is considered a denial-of-service vector for WebAssembly embedders and is thus a security issue in Wasmtime.

This bug does not affect WASIp2 and embedders using components.