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Fencer Vulns
medium 5.0

CVE-2026-34983 json

Wasmtime has a use-after-free bug after cloning `wasmtime::Linker`

published 2026-04-09 7 mo ago modified 2026-10-26 13 d ago also EUVD-2026-21029 , GHSA-hfr4-7c6c-48w2 , PYSEC-2026-151 , RUSTSEC-2026-0090

cvss
5.0
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.1%
EPSS 0.1% chance of exploitation in 30 days, percentile 1%
public exploits
0
none known

Summary

Wasmtime is a runtime for WebAssembly. In 43.0.0, cloning a wasmtime::Linker is unsound and can result in use-after-free bugs. This bug is not controllable by guest Wasm programs. It can only be triggered by a specific sequence of embedder API calls made by the host. Specifically, the following steps must occur to trigger the bug clone a wasmtime::Linker, drop the original linker instance, use the new, cloned linker instance, resulting in a use-after-free. This vulnerability is fixed in 43.0.1.

Patch / fix

  • crates.io wasmtime 43.0.1
  • bytecodealliance wasmtime 43.0.1
  • rust-wasmtime Debian 14 36.0.7+dfsg-1

debian advisories DEBIAN-CVE-2026-34983

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-2026-34983 updated cvss 2.5

wasmtime: Wasmtime: Use-after-free due to unsound linker cloning

  • 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
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
6 mo ago

Exploit prediction

0.12% chance of exploitation in the next 30 days, higher than 1% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hfr4-7c6c-48w2 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 1.0 CVSS:4.0/AV:P/AC:H/AT:P/PR:H/UI:A/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N
CNA 4.0 1.0 CVSS:4.0/AV:P/AC:H/AT:P/PR:H/UI:A/VC:L/VI:L/VA:L/SC:N/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 5.0 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
OSV 3.1 5.0 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
crates.io wasmtime
>=43.0.0, <43.0.1
43.0.1
pypi wasmtime
<=43.0.0
 no fix listed

Affected products

  • bytecodealliance wasmtime

Classification

Weakness

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.