Use After Free in lucet

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.5 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

EPSS

• CVE-2021-43790: 1.62% estimated exploitation activity in the next 30 days; percentile 76.07 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact There is a bug in the main branch of Lucet's lucet-runtime that allows a use-after-free in an Instance object that could result in memory corruption, data race, or other related issues. This bug was introduced early in the development of Lucet and is present in all releases. As a result of this bug, and dependent on the memory backing for the Instance objects, it is possible to trigger a use-after-free when the Instance is dropped. Patches Users should upgrade to the main branch of the Lucet repository. Lucet does not provide versioned releases on crates.io. Workarounds There is no way to remediate this vulnerability without upgrading. Description Lucet uses a "pool" allocator for new WebAssembly instances that are created. This pool allocator manages everything from the linear memory of the wasm instance, the runtime stack for async switching, as well as the memory behind the Instance itself. Instances are referred to via an InstanceHandle type which will, on drop, release…

Published by the source

30 Nov 2021, 22:20 UTC

Last modified by the source

20 Jan 2026, 19:01 UTC

Source last checked

26 Oct 2026, 15:39 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-hf79-8hjp-rrvq

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2021-43790

Advisory: Use After Free in lucet
IDs: CVE-2021-43790, GHSA-hf79-8hjp-rrvq
Record: https://patchnext.com/advisories/cve-2021-43790 (revision 1, source checked 26 Oct 2026, 15:39 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor response not established. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io lucet-runtime: affected <= 0.6.1

## Suggested inspection (read-only)
- crates.io lucet-runtime: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on lucet-runtime.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-hf79-8hjp-rrvq (GitHub-reviewed advisory GHSA-hf79-8hjp-rrvq lists affected ranges: crates.io lucet-runtime >=0 <=0.6.1)

Commands are suggestions: review each one before running it.