CVE-2026-34946
Host panic when Winch compiler executes `table.fill`
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.
How to fix CVE-2026-34946
To remediate CVE-2026-34946, upgrade the affected package to a fixed version below.
- —upgrade to 36.0.7 or later
- —upgrade to 36.0.7 or later
- —no fix listed
Is CVE-2026-34946 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (3)
- >= 25.0.0, < 36.0.7
- >= 0.0.0-0, < 36.0.7, >= 37.0.0, < 42.0.2, >= 43.0.0, < 43.0.1
- from 0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N |
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |