RUSTSEC-2021-0155Published

Use After Free in lucet

Collected exploitation and prediction evidence

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

cve-program · CVE-2021-43790

Published

Lucet is a native WebAssembly compiler and runtime. There is a bug in the main branch of `lucet-runtime` affecting all versions published to crates.io 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. Users should upgrade to the main branch of the Lucet repository. Lucet no longer provides versioned releases on crates.io. There is no way to remediate this vulnerability without upgrading.

Source published: 29 Nov 2021 23:55:10 UTC
Source modified: 4 Aug 2024 04:03:08 UTC
Observed here: 23 Oct 2026 15:48:27 UTC
Source terms: CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

euvd · EUVD-2021-2355

Published

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Nov 29, 2021, 11:55:10 PM

dateUpdated: Aug 4, 2024, 4:03:08 AM

Source published: Nov 29, 2021, 11:55:10 PM (timezone not stated)
Source modified: Aug 4, 2024, 4:03:08 AM (timezone not stated)
Observed here: 9 Nov 2026 23:07:35 UTC
Source terms: ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

nvd · CVE-2021-43790

Published

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Modified

Weakness classifications: CWE-416

Original publisher date fields

published: 2021-11-30T00:15:07.357

lastModified: 2026-06-17T04:11:26.707

1 source CPE criteria · context only

cpe:2.3:a:bytecodealliance:lucet:*:*:*:*:*:rust:*:*

The original JSON retains the logical configuration operators, exclusions and version bounds.

Source published: 30 Nov 2021 00:15:07 UTC
Source modified: 17 Jun 2026 04:11:26 UTC
Observed here: 24 Oct 2026 19:17:31 UTC
Source terms: NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.5 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

CVSS 3.1 · [email protected] · Primary · 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS 2.0 · [email protected] · Primary · 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P

osv · GHSA-hf79-8hjp-rrvq

Published

### 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 the memory backing the Instance back to the pool. When an Instance is dropped, the fields of the `Instance` are destructed top-to-bottom, however when the `alloc: Alloc` field is destructed, the memory backing the `Instance` is released back to the pool before the destructors of the remaining fields are run. If another thread allocates the same memory from the pool while these destructors are still running, a race condition occurs that can lead to use-after-free errors. The bug was corrected by changing how the `InstanceHandle` destructor operates to ensure that the memory backing an Instance is only returned to the pool once the `Instance` has been completely destroyed. This security advisory has been assigned CVE-2021-43790. ### For more information If you have any questions or comments about this advisory: * Open an issue in [lucet repository](https://github.com/bytecodealliance/lucet) * Email [the lucet team](mailto:[email protected]) * See the [Bytecode Alliance security policy](https://bytecodealliance.org/security)

Source published: 30 Nov 2021 22:20:36 UTC
Source modified: 8 Jul 2026 06:29:00 UTC
Observed here: 24 Oct 2026 13:19:54 UTC
Source terms: GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

Publisher rating · HIGH

osv · RUSTSEC-2021-0155

Published

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 the memory backing the Instance back to the pool. When an Instance is dropped, the fields of the Instance are destructed top-to-bottom, however when the alloc: Alloc field is destructed, the memory backing the Instance is released back to the pool before the destructors of the remaining fields are run. If another thread allocates the same memory from the pool while these destructors are still running, a race condition occurs that can lead to use-after-free errors. The bug was corrected by changing how the InstanceHandle destructor operates to ensure that the memory backing an Instance is only returned to the pool once the Instance has been completely destroyed.

Source published: 30 Nov 2021 12:00:00 UTC
Source modified: 12 Oct 2026 18:00:04 UTC
Observed here: 24 Oct 2026 13:19:54 UTC
Source terms: OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H