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Fencer Vulns
medium 6.5

CVE-2026-34945 json

Wasmtime leaks host data with 64-bit tables and Winch

published 2026-04-09 7 mo ago modified 2026-10-26 13 d ago also EUVD-2026-21024 , GHSA-m9w2-8782-2946 , JLSEC-2026-1358 , RUSTSEC-2026-0086

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 27%
public exploits
0
none known

Summary

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.

Patch / fix

  • crates.io wasmtime 36.0.7, 42.0.2, 43.0.1
  • julia Wasmtime_jll 45.0.1+0
  • bytecodealliance wasmtime 36.0.7, 42.0.2, 44.0.1
  • rust-wasmtime Debian 14 36.0.7+dfsg-1

debian advisories DEBIAN-CVE-2026-34945

  • tree-sitter openSUSE Tumbleweed 0.26.8-1.1

opensuse advisories openSUSE-SU-2026:10598-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-34945 updated cvss 5.6

wasmtime: winch: Wasmtime Winch compiler: Information disclosure via incorrect table.size instruction translation

  • Red Hat Connectivity Link 1 redhat-user-workloads/api-management-tenant/rhcl-1-3-wasm-shim Red Hat Enterprise Linux 10 virt-firmware-rs
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 27% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 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
GitHub 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
CNA 4.0 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
OSV 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
crates.io wasmtime
>=25.0.0, <36.0.7
>=37.0.0, <42.0.2
>=43.0.0, <43.0.1
>=0.0.0-0, <36.0.7
36.0.7
42.0.2
43.0.1
julia Wasmtime_jll
>=39.0.0+0, <45.0.1+0
45.0.1+0

Affected products

  • bytecodealliance wasmtime

Classification

Weakness
  • CWE-681 Incorrect Conversion between Numeric Types
  • CWE-200 Exposure of Sensitive Information to an Unauthorized Actor

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.