# CVE-2026-34945: Wasmtime leaks host data with 64-bit tables and Winch > A bug in Wasmtime's Winch compiler allows WebAssembly guests to read sensitive host stack data when using 64-bit tables. - **Severity:** Low 2.3 (`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`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 9 Apr 2026 - **Updated:** 10 Apr 2026 - **Also known as:** DEBIAN-CVE-2026-34945, GHSA-m9w2-8782-2946, JLSEC-2026-1358, RUSTSEC-2026-0086, UBUNTU-CVE-2026-34945, openSUSE-SU-2026:10598-1 ## What is CVE-2026-34945? CVE-2026-34945 is a low-severity vulnerability in bytecodealliance wasmtime, published on 9 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim. ### Official 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. Weakness: CWE-681 (Incorrect Conversion between Numeric Types) ## Which versions are affected by CVE-2026-34945? 7 open source packages ship an affected version, including wasmtime. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `wasmtime` | crates.io | From 0.0.0-0 | 36.0.7, 42.0.2, 43.0.1 | | `wasmtime` | crates.io | From 25.0.0 | 36.0.7 | | `wasmtime` | crates.io | From 25.0.0 | 36.0.7 | | `wasmtime` | crates.io | From 37.0.0 | 42.0.2 | | `wasmtime` | crates.io | From 37.0.0 | 42.0.2 | | `wasmtime` | crates.io | From 43.0.0 | 43.0.1 | | `wasmtime` | crates.io | From 43.0.0 | 43.0.1 | | `tree-sitter` | openSUSE:Tumbleweed | All versions | 0.26.8-1.1 | Products: Bytecodealliance Wasmtime. ## How do I fix CVE-2026-34945? Upgrade wasmtime to a fixed version for your release line: 36.0.7, 42.0.2 or 43.0.1. ## Is CVE-2026-34945 being exploited? There is no known exploitation of CVE-2026-34945 in the wild and no public exploit code. ## Other vulnerabilities in bytecodealliance wasmtime - [CVE-2026-34971](https://insights.sbomify.com/CVE-2026-34971/): Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift (critical 9.0) - [CVE-2026-34987](https://insights.sbomify.com/CVE-2026-34987/): Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access (critical 9.0) - [CVE-2022-39393](https://insights.sbomify.com/CVE-2022-39393/): Wasmtime vulnerable to data leakage between instances in the pooling allocator (high 8.6) - [CVE-2022-24791](https://insights.sbomify.com/CVE-2022-24791/): Use after free in Wasmtime (high 8.1) - [CVE-2026-47261](https://insights.sbomify.com/CVE-2026-47261/): Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction (high 7.5) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-34945 and fix it if it is affected. What it is: CVE-2026-34945 is a low-severity vulnerability in bytecodealliance wasmtime, published on 9 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-34945 in the wild and no public exploit code. Affected packages and fixed versions: - wasmtime (crates.io): affected from 0.0.0-0; fixed in 36.0.7, 42.0.2, 43.0.1 - wasmtime (crates.io): affected from 25.0.0; fixed in 36.0.7 - wasmtime (crates.io): affected from 25.0.0; fixed in 36.0.7 - wasmtime (crates.io): affected from 37.0.0; fixed in 42.0.2 - wasmtime (crates.io): affected from 37.0.0; fixed in 42.0.2 - wasmtime (crates.io): affected from 43.0.0; fixed in 43.0.1 - wasmtime (crates.io): affected from 43.0.0; fixed in 43.0.1 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-34945/ (Markdown: https://insights.sbomify.com/CVE-2026-34945/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34945 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34945 - OSV: https://osv.dev/vulnerability/CVE-2026-34945 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-34945/ Summaries are generated and may contain mistakes; the official description above is the record.