CVE-2026-34945

Workarounds

Users of Cranelift are not affected by this issue, but users of Winch have no workarounds other than disabling the Config::wasm_memory64 proposal.

Wasmtime's Winch compiler contains a bug where a 64-bit table, part of the memory64 proposal of WebAssembly, incorrectly translated the table.size instruction. This bug could lead to disclosing data on the host's stack to WebAssembly guests. The host's stack can possibly contain sensitive data related to other host-originating operations which is not intended to be disclosed to guests.

This bug specifically arose from a mistake where the return value of table.size was statically typed as a 32-bit integer, as opposed to consulting the table's index type to see how large the returned register could be. When combined with details about Wnich's ABI, such as multi-value returns, this can be combined to read stack data from the host, within a guest. This information disclosure should not be possible in WebAssembly, violates spec semantics, and is a vulnerability in Wasmtime.

CVE-2026-34945 has a CVSS score of 6.5 (Low). The vector is network-reachable, low 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-2026-34945? CVE-2026-34945 is a low-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-2026-34945? CVE-2026-34945 has a CVSS score of 6.5 (Low). 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-2026-34945? wasmtime (rust) versions >= 25.0.0, < 36.0.7 is affected.
4. Is there a fix for CVE-2026-34945? Yes. CVE-2026-34945 is fixed in 36.0.7, 42.0.2, 43.0.1. Upgrade to this version or later.
5. Is CVE-2026-34945 exploitable, and should I be worried? Whether CVE-2026-34945 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-2026-34945 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-2026-34945?
   • Upgrade wasmtime to 36.0.7 or later
   • Upgrade wasmtime to 42.0.2 or later
   • Upgrade wasmtime to 43.0.1 or later