Wasmtime leaks host data with 64-bit tables and Winch
Published Apr 9, 2026
2.3
LOWCVSS 4.0
EPSS 0.38%
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.
Affected products
-
- Version >= 25.0.0, < 36.0.7StatusaffectedConstraints-
- Version >= 37.0.0, < 42.0.2StatusaffectedConstraints-
- Version >= 43.0.0, < 44.0.1StatusaffectedConstraints-
- Version
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Bytecodealliance | Wasmtime | n/a |
|
- ≥ 25.0.0 · < 36.0.7
- ≥ 37.0.0 · < 42.0.2
- ≥ 43.0.0 · < 43.0.1
No data.
Red Hat Connectivity Link 1
redhat-user-workloads/rhcl-1-3-wasm-shim
Fix deferred
Red Hat Enterprise Linux 10
virt-firmware-rs
Fix deferred
| Product | Package | State | Advisory |
|---|---|---|---|
| Red Hat Connectivity Link 1 | redhat-user-workloads/rhcl-1-3-wasm-shim | Fix deferred | n/a |
| Red Hat Enterprise Linux 10 | virt-firmware-rs | Fix deferred | n/a |
No package ranges for this CVE.
Remediation
Red Hat mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
References (8)
- https://access.redhat.com/security/cve/CVE-2026-34945 Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=2457004 Issue Tracking
- https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-21024 Advisory
- https://github.com/advisories/GHSA-m9w2-8782-2946 Advisory
- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946 x_refsource_CONFIRMVendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-34945
- https://rustsec.org/advisories/RUSTSEC-2026-0086.html
- https://www.cve.org/CVERecord?id=CVE-2026-34945
Change history (0)
No recorded changes yet.