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Fencer Vulns
high 7.5

CVE-2026-34943 json

Wasmtime panics when lifting `flags` component value

published 2026-04-09 7 mo ago modified 2026-10-26 13 d ago also EUVD-2026-21022 , GHSA-m758-wjhj-p3jq , JLSEC-2026-1356 , RUSTSEC-2026-0085

cvss
7.5
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. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime contains a possible panic which can happen when a flags-typed component model value is lifted with the Val type. If bits are set outside of the set of flags the component model specifies that these bits should be ignored but Wasmtime will panic when this value is lifted. This panic only affects wasmtime's implementation of lifting into Val, not when using the flags! macro. This additionally only affects flags-typed values which are part of a WIT interface. This has the risk of being a guest-controlled panic within the host which Wasmtime considers a DoS vector. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.

Patch / fix

  • crates.io wasmtime 24.0.7, 36.0.7, 42.0.2, 43.0.1
  • julia Wasmtime_jll 45.0.1+0
  • bytecodealliance wasmtime 24.0.7, 36.0.7, 42.0.2, 44.0.1
  • rust-wasmtime Debian 14 36.0.7+dfsg-1

debian advisories DEBIAN-CVE-2026-34943

  • tree-sitter openSUSE Tumbleweed 0.26.8-2.1

opensuse advisories openSUSE-SU-2026:10715-1

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-2026-34943 updated cvss 5.0

Wasmtime: Wasmtime: Denial of Service due to malformed flags-typed component model value processing

  • Red Hat Connectivity Link 1 redhat-user-workloads/api-management-tenant/rhcl-1-3-wasm-shim
    affected: workaround, no fix available
  • Red Hat Enterprise Linux 10 virt-firmware-rs
    not affected: component not present

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
yes
Technical impact
partial
Assessed
6 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 5.6 CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 4.0 5.6 CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:A/VC:N/VI:N/VA:H/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 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
crates.io wasmtime
<24.0.7
>=25.0.0, <36.0.7
>=37.0.0, <42.0.2
>=43.0.0, <43.0.1
>=0.0.0-0, <24.0.7
24.0.7
36.0.7
42.0.2
43.0.1
julia Wasmtime_jll
<45.0.1+0
45.0.1+0

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.