CVE-2026-115380 in Wasmtime
Summary
by MITRE • 10/23/2026
Wasmtime before 36.0.17, 37.0.0 before 48.0.4, and 49.0.0 before 49.0.2 contains a denial of service vulnerability in the wasmtime-wasi WASI preview 0 poll_oneoff adapter, which performs O(n) host work per subscription without consuming or checking fuel. Malicious guest modules can pass many subscriptions to force long-running host computation that ignores configured fuel limits.
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Analysis
by VulDB Data Team • 10/23/2026
The identified security flaw resides within the wasmtime-wasi component of Wasmtime versions prior to 36.0.17, 37.0.0 through 48.0.4, and 49.0.0 through 49.0.2. This vulnerability specifically affects the implementation of the WASI preview zero poll_oneoff adapter, which is responsible for handling asynchronous I/O operations in WebAssembly environments. The core technical deficiency lies in how this adapter manages computational resources during subscription processing. When a guest module invokes the poll_oneoff function to wait on multiple file descriptors or events simultaneously, the underlying host-side implementation performs work that scales linearly with the number of subscriptions provided by the caller. Crucially, this execution path fails to consume fuel from the WebAssembly runtime's configured budget and does not actively check for fuel exhaustion during the processing loop.
In a standard secure WebAssembly environment, the concept of fuel is essential for preventing infinite loops or excessive computation that could lead to denial of service conditions. Fuel acts as a metering mechanism where each computational step consumes a unit of energy, ensuring that guest modules cannot monopolize host resources indefinitely. However, in this specific vulnerability scenario, an attacker can craft a malicious WebAssembly module that passes a large number of subscriptions to the poll_oneoff adapter. Because the host-side processing ignores these fuel limits, the runtime will continue executing the necessary system calls and state checks for every subscription until completion, regardless of how much computational budget has been allocated by the sandboxing environment or application developer.
The operational impact of this flaw is a significant denial of service against the hosting process. Since the malicious guest module can force long-running host computation without being interrupted by fuel exhaustion mechanisms, it effectively bypasses the primary safeguard designed to protect system stability. This allows an untrusted WebAssembly component to consume excessive CPU cycles and potentially block other concurrent operations within the same runtime instance. In server-side deployments or multi-tenant environments where Wasmtime is used for isolation, this vulnerability could allow a single compromised or malicious module to degrade performance for all other modules running in the same process, leading to service unavailability or severe latency increases.
From a classification perspective, this issue aligns with CWE-400, which describes Uncontrolled Resource Consumption, as the application fails to properly control the allocation and use of system resources based on user input. Furthermore, it relates to CWE-675, Deprecated Features, in the context of using outdated or improperly implemented security controls like fuel metering within specific API adapters. In terms of adversary tactics, this vulnerability supports techniques associated with MITRE ATT&CK T1499, Endpoint Denial of Service, where an attacker leverages resource exhaustion to disrupt availability rather than seeking data exfiltration or privilege escalation at the immediate stage.
To mitigate this risk, organizations and developers must upgrade Wasmtime to version 36.0.17 or later for the older release line, version 48.0.4 or later for the thirty-seven series, and version 49.0.2 or later for the forty-nine series. These updated versions contain patches that ensure the poll_oneoff adapter correctly accounts for fuel consumption during subscription processing, thereby restoring the integrity of the resource metering system. Additionally, until an upgrade is feasible, administrators should consider implementing strict limits on the number of subscriptions allowed per invocation at the application layer or utilizing runtime configurations that enforce stricter timeouts and execution budgets to compensate for the missing internal checks in older versions.