CVE-2021-39219

Memory unsafety via cross-Engine Linker type confusion

Published Sep 17, 2021 · Updated Aug 4, 2024

Type confusion in Wasmtime before 0.30.0 allows local users to invoke host functions with the wrong type through cross-Engine Linker use. Linker::func_* registered a host trampoline without verifying that its Engine matched the Store Engine, leaving the recorded type information inconsistent with the function pointer. Reachability requires an embedding to create a Linker and Store from different Engine values and instantiate a module through that Linker.

CVSS severity6.3
Medium
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Type confusion in Wasmtime before 0.30.0 allows local users to invoke host functions with the wrong type through cross-Engine Linker use. Linker::func_* registered a host trampoline without verifying that its Engine matched the Store Engine, leaving the recorded type information inconsistent with the function pointer. Reachability requires an embedding to create a Linker and Store from different Engine values and instantiate a module through that Linker.

The record

CVE
CVE-2021-39219
Published
Sep 17, 2021
Updated
Aug 4, 2024
Vendor
Bytecode Alliance
Product
Wasmtime
Classifications
CWE-843
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Sep 17, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<= 0.29.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesUnavailable in this record.

What is affected?

Bytecode Alliance · Wasmtimeversion=<= 0.29.0

Published CVSS scores

3.3NIST NVDAV:L/AC:M/Au:N/C:N/I:P/A:P
6.3GitHub, Inc.CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:H
6.3NIST NVDCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-843Access of Resource Using Incompatible Type ('Type Confusion')

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo