# CVE-2021-43790: Use After Free in lucet

> A use-after-free bug in the Lucet WebAssembly runtime allows attackers to trigger memory corruption or crashes when an Instance object is dropped.

- **Severity:** High 8.5 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 29 Nov 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-hf79-8hjp-rrvq, RUSTSEC-2021-0155

## What is CVE-2021-43790?

CVE-2021-43790 is a high-severity use after free vulnerability in bytecodealliance lucet, published on 29 Nov 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

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.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-43790?

3 open source packages ship an affected version, including lucet-runtime. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `lucet-runtime` | crates.io | All versions to 0.6.1 | None |
| `lucet-runtime` | crates.io | All versions to 0.6.1 | None |
| `lucet-runtime` | crates.io | From 0.0.0-0 | None |

Products: Bytecodealliance Lucet.

## How do I fix CVE-2021-43790?

No fix has been published for CVE-2021-43790 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-43790 being exploited?

There is no known exploitation of CVE-2021-43790 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-43790 and fix it if it is affected.

What it is: CVE-2021-43790 is a high-severity use after free vulnerability in bytecodealliance lucet, published on 29 Nov 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-43790 in the wild and no public exploit code.

Affected packages and fixed versions:
- lucet-runtime (crates.io): affected all versions up to 0.6.1; no fix listed
- lucet-runtime (crates.io): affected all versions up to 0.6.1; no fix listed
- lucet-runtime (crates.io): affected from 0.0.0-0; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-43790/ (Markdown: https://insights.sbomify.com/CVE-2021-43790/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43790
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43790
- OSV: https://osv.dev/vulnerability/CVE-2021-43790

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43790/
Summaries are generated and may contain mistakes; the official description above is the record.