Wasmtime is a runtime environment for executing WebAssembly (WASM) modules, providing WASI (WebAssembly System Interface) host interfaces that allow guest modules to interact with host system resources. CVE-2026-27204 identifies a vulnerability where Wasmtime versions prior to 24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0 do not adequately restrict resource allocations requested by guest WASM modules. This lack of proper resource management enables guest modules to request excessive resources, leading to uncontrolled resource consumption on the host system. The vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption) and related CWEs (CWE-770, CWE-774, CWE-789) that describe improper handling of resource allocation and limits. The issue manifests as a Denial of Service (DoS) vector, where a malicious or compromised guest module can exhaust CPU, memory, or other critical resources, causing the host to degrade or crash. Although fixed versions have been released, the default configurations do not enable the resource limiting knobs to maintain backward compatibility, so embedders must explicitly enable these protections. No known exploits are currently reported in the wild, but the vulnerability poses a significant risk in environments where untrusted or semi-trusted WASM modules are executed. The CVSS 4.0 base score is 6.9 (medium), reflecting network attack vector, low attack complexity, partial privileges required, user interaction needed, and high impact on availability without affecting confidentiality or integrity.

The primary impact of this vulnerability is Denial of Service (DoS) through resource exhaustion on hosts running vulnerable Wasmtime versions. Organizations embedding Wasmtime to run WebAssembly modules—especially those accepting untrusted or third-party WASM code—face risks of service disruption, degraded performance, or crashes. This can affect cloud providers, edge computing platforms, serverless environments, and any software leveraging Wasmtime for sandboxed execution. The availability impact can cascade to dependent services and users, potentially causing downtime and operational losses. Since confidentiality and integrity are not directly impacted, data breaches or unauthorized modifications are unlikely from this vulnerability alone. However, DoS conditions can be exploited as part of multi-stage attacks or to distract defenders. The lack of default protective configurations in fixed versions means organizations must proactively configure resource limits to fully mitigate the risk. Failure to do so leaves systems vulnerable despite running patched versions.

To mitigate CVE-2026-27204, organizations should upgrade Wasmtime to version 24.0.6, 36.0.6, 40.0.4, 41.0.4, 42.0.0 or later. After upgrading, embedders must explicitly enable and tune resource limiting knobs provided by Wasmtime to enforce strict caps on CPU, memory, and other resource usage by guest WASM modules. This includes configuring maximum memory allocation, CPU time quotas, and other relevant limits based on the deployment context and expected workload. Embedders should audit their embedding configurations to ensure these limits are active and tested under realistic load scenarios. Monitoring resource usage and setting alerts for abnormal consumption patterns can help detect exploitation attempts early. Additionally, restricting the execution of untrusted or unknown WASM modules and applying network-level protections can reduce exposure. Since no workarounds exist without upgrading, timely patching combined with configuration hardening is critical. Developers should also stay informed about Wasmtime updates and security advisories to apply future fixes promptly.