CVE-2026-119137 in Wasmtime
Summary
by MITRE • 10/29/2026
Wasmtime 42.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a stack overflow vulnerability that allows guests to crash the host through recursive type drops. Guests can define a long chain of recursive types so that removing the top-level type triggers unbounded recursive drops, exhausting the host stack.
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Analysis
by VulDB Data Team • 10/30/2026
The WebAssembly runtime environment Wasmtime is susceptible to a critical stack exhaustion vulnerability affecting versions prior to 48.0.6 and 49.0.3. This flaw stems from an improper handling of type system operations during garbage collection, specifically within the mechanism responsible for dropping or deallocating complex data structures defined by guest applications. The core technical deficiency lies in how the runtime processes recursive type definitions when they are removed from memory. When a WebAssembly module defines a long chain of mutually recursive types, the internal logic required to clean up these structures fails to implement adequate depth limits or iterative safeguards for the deallocation process.
When an application triggers the removal of a top-level type that is part of such a recursive structure, the runtime initiates a cascade of drop operations intended to free associated memory and resources. Due to the lack of recursion bounds checking, this cleanup procedure descends into unbounded depth rather than terminating after processing all reachable nodes in a controlled manner. Each level of recursion consumes stack space on the host system where Wasmtime is executing. As the runtime attempts to unwind these deeply nested references, it rapidly depletes the available call stack allocated for that execution context.
The operational impact of this vulnerability is severe and immediate. Because the exhaustion occurs within the main execution thread or worker threads managing WebAssembly instances, the result is a deterministic crash of the host process rather than a graceful error return to the guest application. This constitutes a denial-of-service condition where an attacker can reliably bring down services running Wasmtime by crafting malicious modules with deeply nested recursive type definitions. The vulnerability effectively allows untrusted code executed within the sandboxed environment to compromise the stability and availability of the underlying host system, violating the fundamental isolation guarantees expected from WebAssembly runtimes.
From a classification perspective, this issue aligns with CWE-675, which describes operations on data structures that are susceptible to denial-of-service via resource exhaustion through unbounded recursion or iteration. It also maps to MITRE ATT&CK technique T1499, specifically Endpoint Denial of Service, as the attacker leverages a software flaw to disrupt service availability without necessarily gaining unauthorized access to sensitive data. The attack vector is remote if Wasmtime is deployed in server-side environments that accept untrusted WebAssembly modules from network sources, making this particularly dangerous for cloud-native and edge computing deployments.
Mitigation strategies must prioritize immediate version upgrades to address the root cause within the runtime engine itself. Administrators running affected versions of Wasmtime should upgrade to 48.0.6 or later, or 49.0.3 and beyond, where developers have implemented safeguards such as recursion depth limits or iterative stack unwinding algorithms to prevent unbounded growth during type dropping operations. In environments where upgrading is not immediately feasible, defensive measures include implementing strict validation of WebAssembly modules before execution to reject those with excessively deep recursive structures. Additionally, configuring the host operating system and runtime environment with stricter memory protection policies can help contain the impact by limiting stack size allocations for Wasmtime processes, thereby reducing the window of opportunity for successful exploitation while maintaining service continuity through redundancy or failover mechanisms.