# CVE-2021-47865: ProFTPD 1.3.7a - Remote Denial of Service

> Attackers can cause denial of service in ProFTPD by exhausting connection limits through multiple simultaneous FTP connections.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 21 Jan 2026
- **Updated:** 7 Apr 2026
- **Also known as:** GHSA-mf77-27mv-mhm4, UBUNTU-CVE-2021-47865

## What is CVE-2021-47865?

CVE-2021-47865 is a high-severity denial of service vulnerability in ProFTPD, published on 21 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

ProFTPD 1.3.7a contains a denial of service vulnerability that allows attackers to overwhelm the server by creating multiple simultaneous FTP connections. Attackers can repeatedly establish connections using threading to exhaust server connection limits and block legitimate user access.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2021-47865?


## How do I fix CVE-2021-47865?

No fix has been published for CVE-2021-47865 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-47865 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-47865 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-47865 and fix it if it is affected.

What it is: CVE-2021-47865 is a high-severity denial of service vulnerability in ProFTPD, published on 21 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-47865 exists.

Affected product: ProFTPD. 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-2021-47865/ (Markdown: https://insights.sbomify.com/CVE-2021-47865/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47865
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47865
- OSV: https://osv.dev/vulnerability/CVE-2021-47865

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47865/
Summaries are generated and may contain mistakes; the official description above is the record.