# CVE-2021-3750: Use after free in QEMU

> A malicious guest can trigger a use-after-free in QEMU's USB EHCI emulation to crash the host or execute arbitrary code.

- **Severity:** High 8.2 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 May 2022
- **Updated:** 3 Aug 2024
- **Also known as:** AZL-35151, AZL-9701, DEBIAN-CVE-2021-3750, GHSA-2v3x-7c37-r5r2, OESA-2022-1679, UBUNTU-CVE-2021-3750

## What is CVE-2021-3750?

CVE-2021-3750 is a high-severity use after free vulnerability in Qemu Qemu, published on 2 May 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A DMA reentrancy issue was found in the USB EHCI controller emulation of QEMU. EHCI does not verify if the Buffer Pointer overlaps with its MMIO region when it transfers the USB packets. Crafted content may be written to the controller's registers and trigger undesirable actions (such as reset) while the device is still transferring packets. This can ultimately lead to a use-after-free issue. A malicious guest could use this flaw to crash the QEMU process on the host, resulting in a denial of service condition, or potentially execute arbitrary code within the context of the QEMU process on the host. This flaw affects QEMU versions before 7.0.0.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-3750?

It affects 2 products.


Products: Qemu Qemu, Redhat Enterprise Linux.

## How do I fix CVE-2021-3750?

Upgrade to a fixed version.

## Is CVE-2021-3750 being exploited?

There is no known exploitation of CVE-2021-3750 in the wild and no public exploit code.

## Other vulnerabilities in Qemu Qemu

- [CVE-2022-36648](https://insights.sbomify.com/CVE-2022-36648/): Null dereference in n/a (critical 10.0)
- [CVE-2015-8556](https://insights.sbomify.com/CVE-2015-8556/): Race condition in n/a (critical 10.0)
- [CVE-2009-3616](https://insights.sbomify.com/CVE-2009-3616/): Use after free in n/a (critical 9.9)
- [CVE-2019-12928](https://insights.sbomify.com/CVE-2019-12928/): Command injection in n/a (critical 9.8)
- [CVE-2019-12929](https://insights.sbomify.com/CVE-2019-12929/): Command injection in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3750 and fix it if it is affected.

What it is: CVE-2021-3750 is a high-severity use after free vulnerability in Qemu Qemu, published on 2 May 2022. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-3750 in the wild and no public exploit code.

Affected product: Qemu Qemu. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2021-3750/ (Markdown: https://insights.sbomify.com/CVE-2021-3750/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3750
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3750
- OSV: https://osv.dev/vulnerability/CVE-2021-3750

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3750/
Summaries are generated and may contain mistakes; the official description above is the record.