# CVE-2026-22321: Stack-Based Buffer Overflow in CLI Login Username Handling over CLI

> Unauthenticated attackers can cause a denial of service by sending oversized usernames to the CLI login, crashing the session thread.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Mar 2026
- **Updated:** 18 Mar 2026
- **Also known as:** GHSA-j66g-mfcw-hrf3

## What is CVE-2026-22321?

CVE-2026-22321 is a medium-severity memory corruption vulnerability in Phoenix Contact FL NAT 2008, published on 18 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A stack-based buffer overflow in the device's Telnet/SSH CLI login routine occurs when a unauthenticated attacker send an oversized or unexpected username input. An overflow condition crashes the thread handling the login attempt, forcing the session to close. Because other CLI sessions remain unaffected, the impact is limited to a low‑severity availability disruption.

Weakness: CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-22321?


## How do I fix CVE-2026-22321?

No fix has been published for CVE-2026-22321 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-22321 being exploited?

There is no known exploitation of CVE-2026-22321 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-22321 and fix it if it is affected.

What it is: CVE-2026-22321 is a medium-severity memory corruption vulnerability in Phoenix Contact FL NAT 2008, published on 18 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-22321 in the wild and no public exploit code.

Affected product: Phoenix Contact FL NAT 2008. 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-2026-22321/ (Markdown: https://insights.sbomify.com/CVE-2026-22321/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-22321
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-22321
- OSV: https://osv.dev/vulnerability/CVE-2026-22321

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-22321/
Summaries are generated and may contain mistakes; the official description above is the record.