CVE-2025-53901 is a vulnerability identified in the Wasmtime runtime for WebAssembly, specifically affecting versions prior to 24.0.4, 33.0.2, and 34.0.2. Wasmtime implements WASIp1 import functions through its wasmtime-wasi crate. The vulnerability arises from improper handling of file descriptor operations, specifically when a WebAssembly guest calls the `fd_renumber` function with either two identical arguments or when the second argument matches a previously closed file descriptor number. This misuse corrupts the internal state of Wasmtime's file descriptor management. Subsequently, invoking `path_open` to open a new file descriptor triggers a panic in the host runtime due to this corrupted state. Although this panic causes a denial-of-service (DoS) condition by crashing the host, it does not lead to memory corruption, heap corruption, or sandbox escape, preserving the integrity and confidentiality of the host system. The vulnerability requires the attacker to have the ability to execute a crafted sequence of WASI calls, including `fd_renumber` and `path_open`, which is possible only if the WebAssembly guest has access to preopened directories—a common scenario in many Wasmtime embeddings. Notably, this issue does not affect WASIp2 or embedders using components, nor those that restrict guest capabilities to open new file descriptors. There is no known workaround other than upgrading to patched versions 24.0.4, 33.0.2, or 34.0.2. The CVSS v3.1 base score is 3.5 (low severity), reflecting the limited impact (denial of service only), network attack vector, low attack complexity, requirement for privileges (PR:L), and user interaction (UI:R). No known exploits are reported in the wild as of publication.

For European organizations, the primary impact of CVE-2025-53901 is a potential denial-of-service condition in applications or services embedding Wasmtime to run WebAssembly workloads. This could disrupt critical services relying on WebAssembly for sandboxed execution, such as serverless platforms, edge computing nodes, or embedded systems that utilize Wasmtime for extensibility or plugin architectures. While the vulnerability does not compromise data confidentiality or integrity, repeated or targeted exploitation could degrade service availability, leading to operational interruptions and potential financial or reputational damage. Organizations deploying Wasmtime in multi-tenant environments or exposed to untrusted WebAssembly modules are at higher risk. Given the growing adoption of WebAssembly in cloud-native and edge environments across Europe, especially in sectors like finance, telecommunications, and manufacturing, this vulnerability could affect service reliability if unpatched. However, the requirement for specific guest capabilities and the absence of memory corruption limit the scope of impact to denial-of-service scenarios only.

The definitive mitigation is to upgrade all Wasmtime deployments to the patched versions 24.0.4, 33.0.2, or 34.0.2 as appropriate. Organizations should audit their use of Wasmtime to identify embeddings that expose WASIp1 interfaces with preopened directories allowing file descriptor creation. Where upgrading is temporarily not feasible, consider restricting guest capabilities to prevent opening new file descriptors or disable the use of `fd_renumber` if possible. Embedders using WASIp2 or component-based embeddings are not affected and should verify their configurations accordingly. Additionally, implement runtime monitoring to detect abnormal panics or crashes in Wasmtime hosts, enabling rapid incident response. Incorporate WebAssembly module validation and sandboxing best practices to limit the ability of untrusted modules to invoke problematic sequences. Finally, maintain up-to-date inventories of Wasmtime versions in use and integrate vulnerability scanning into CI/CD pipelines to ensure timely patch application.