What is CVE-2026-34945?

CVE-2026-34945 is a medium-severity vulnerability in Bytecodealliance Wasmtime, classified under Incorrect Conversion between Numeric Types. CVSS score: 6.5/10. Published 2026-04-09.

How severe is CVE-2026-34945?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Bytecodealliance Wasmtime

CVE-2026-34945

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.

EPSS: 0.003 (24.9th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.

Affected products

Bytecodealliance Wasmtime — versions >= 25.0.0, < 36.0.7, >= 37.0.0, < 42.0.2, >= 43.0.0, < 44.0.1

Weakness classification (CWE)

CWE-681 — Incorrect Conversion between Numeric Types

References

security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)

Frequently asked questions

What is CVE-2026-34945?: CVE-2026-34945 is a medium-severity vulnerability in Bytecodealliance Wasmtime, classified under Incorrect Conversion between Numeric Types. CVSS score: 6.5/10. Published 2026-04-09.
How severe is CVE-2026-34945?: Medium severity. CVSS v3 base score is 6.5 out of 10.