What’s Vulnerable › Vulnerabilities
CVE-2026-34946: Wasmtime's host panics when Winch compiler executes `table.fill`
- Severity: high (CVSS 7.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-04-09 · updated 2026-10-26
- Weakness: CWE-670
Description
Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Winch compiler contains a vulnerability where the compilation of the table.fill instruction can result in a host panic. This means that a valid guest can be compiled with Winch, on any architecture, and cause the host to panic. This represents a denial-of-service vulnerability in Wasmtime due to guests being able to trigger a panic. The specific issue is that a historical refactoring changed how compiled code referenced tables within the table.* instructions. This refactoring forgot to update the Winch code paths associated as well, meaning that Winch was using the wrong indexing scheme. Due to the feature support of Winch the only problem that can result is tables being mixed up or nonexistent tables being used, meaning that the guest is limited to panicking the host (using a nonexistent table), or executing spec-incorrect behavior and modifying the wrong table. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.
Affected products
- bytecodealliance wasmtime: from 25.0.0 before 36.0.7; from 37.0.0 before 42.0.2; from 43.0.0 before 43.0.1 — fixed in 36.0.7, 42.0.2, 43.0.1
How to fix
Upgrade to a fixed version: bytecodealliance wasmtime 36.0.7, 42.0.2, 43.0.1. Check the vendor advisory for mitigations.
References
Get alerted when CVE-2026-34946 or the next vulnerability affects your stack