CVE-2026-34946

Workarounds

Users of Cranelift are not affected by this issue, but for users of Winch there is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.

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, #11254, 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.

CVE-2026-34946 has a CVSS score of 7.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (36.0.7, 42.0.2, 43.0.1); upgrading removes the vulnerable code path.

Kodem intelligence

Wasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

1. What is CVE-2026-34946? CVE-2026-34946 is a medium-severity security vulnerability in wasmtime (rust), affecting versions >= 25.0.0, < 36.0.7. It is fixed in 36.0.7, 42.0.2, 43.0.1.
2. How severe is CVE-2026-34946? CVE-2026-34946 has a CVSS score of 7.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of wasmtime are affected by CVE-2026-34946? wasmtime (rust) versions >= 25.0.0, < 36.0.7 is affected.
4. Is there a fix for CVE-2026-34946? Yes. CVE-2026-34946 is fixed in 36.0.7, 42.0.2, 43.0.1. Upgrade to this version or later.
5. Is CVE-2026-34946 exploitable, and should I be worried? Whether CVE-2026-34946 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34946 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34946?
   • Upgrade wasmtime to 36.0.7 or later
   • Upgrade wasmtime to 42.0.2 or later
   • Upgrade wasmtime to 43.0.1 or later