# CVE-2021-3716: Other in nbdkit

> A Man-in-the-Middle attacker can inject plaintext NBD options to terminate client sessions, causing denial of service in nbdkit.

- **Severity:** Low 3.1 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 Mar 2022
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3716, GHSA-3vpg-mwgf-4jvj, UBUNTU-CVE-2021-3716, openSUSE-SU-2024:11078-1

## What is CVE-2021-3716?

CVE-2021-3716 is a low-severity vulnerability in Redhat Enterprise Linux, published on 2 Mar 2022. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A flaw was found in nbdkit due to to improperly caching plaintext state across the STARTTLS encryption boundary. A MitM attacker could use this flaw to inject a plaintext NBD_OPT_STRUCTURED_REPLY before proxying everything else a client sends to the server, potentially leading the client to terminate the NBD session. The highest threat from this vulnerability is to system availability.

Weakness: CWE-924 (Improper Enforcement of Message Integrity During Transmission in a Communication Channel)

## Which versions are affected by CVE-2021-3716?

It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `nbdkit` | openSUSE:Tumbleweed | All versions | 1.27.8-1.2 |

Products: Nbdkit Project Nbdkit, Redhat Enterprise Linux.

## How do I fix CVE-2021-3716?

Apply the vendor's patch.

## Is CVE-2021-3716 being exploited?

There is no known exploitation of CVE-2021-3716 in the wild and no public exploit code.

## Other vulnerabilities in Redhat Enterprise Linux

- [CVE-2025-47711](https://insights.sbomify.com/CVE-2025-47711/): Nbdkit: nbdkit-server: off-by-one error when processing block status may lead to a denial of service (medium 6.5)
- [CVE-2025-47712](https://insights.sbomify.com/CVE-2025-47712/): Nbd: nbdkit: integer overflow triggers an assertion resulting in denial of service (medium 6.5)
- [CVE-2019-14851](https://insights.sbomify.com/CVE-2019-14851/): Denial of service in nbdkit (medium 6.5)
- [CVE-2019-14850](https://insights.sbomify.com/CVE-2019-14850/): Denial of service in nbdkit (low 3.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3716 and fix it if it is affected.

What it is: CVE-2021-3716 is a low-severity vulnerability in Redhat Enterprise Linux, published on 2 Mar 2022. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-3716 in the wild and no public exploit code.

Affected product: Redhat Enterprise Linux. 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-2021-3716/ (Markdown: https://insights.sbomify.com/CVE-2021-3716/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3716
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3716
- OSV: https://osv.dev/vulnerability/CVE-2021-3716

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3716/
Summaries are generated and may contain mistakes; the official description above is the record.