# CVE-2026-6643: A stack-based buffer overflow vulnerability in the VPN Clients on the ADM

> An authenticated remote attacker can execute arbitrary code via a stack-based buffer overflow in ASUSTOR ADM VPN clients.

- **Severity:** High 8.6 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 20 Apr 2026
- **Updated:** 20 Apr 2026
- **Also known as:** GHSA-46vm-f48w-xhvv

## What is CVE-2026-6643?

CVE-2026-6643 is a high-severity memory corruption vulnerability in ASUSTOR Inc. ADM, published on 20 Apr 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

A stack-based buffer overflow vulnerability was found in the VPN Clients on the ADM. The issue stems from the use of unbounded sscanf() and passing user-controlled data directly to printf(). Due to the lack of PIE and Stack Canary protections, an authenticated remote attacker can exploit these to execute arbitrary code as the web server user. 
Affected products and versions include: from ADM 4.1.0 through ADM 4.3.3.RR42 as well as from ADM 5.0.0 through ADM 5.1.2.REO1.

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

## Which versions are affected by CVE-2026-6643?

It affects 1 product.


Products: Asustor Data Master.

## How do I fix CVE-2026-6643?

No fix has been published for CVE-2026-6643 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-6643 being exploited?

There is no known exploitation of CVE-2026-6643 in the wild and no public exploit code.

Public exploit code:

- ASUSTOR ADM 5.1.2 vpnupload.cgi Format String & Stack Buffer Overflow RCE (CVE-2026-6643) (github_poc): https://github.com/mlgzackfly/CVE-2026-6643

## Other vulnerabilities in ASUSTOR Inc. ADM

- [CVE-2018-12313](https://insights.sbomify.com/CVE-2018-12313/): Command injection in n/a (critical 9.8)
- [CVE-2026-24936](https://insights.sbomify.com/CVE-2026-24936/): An improper input validation vulnerability was found in ADM while joining a AD Domain. (critical 9.5)
- [CVE-2026-6644](https://insights.sbomify.com/CVE-2026-6644/): A command injection vulnerability was found in the PPTP VPN Clients on the ADM (critical 9.4)
- [CVE-2026-3179](https://insights.sbomify.com/CVE-2026-3179/): A path traversal vulnerability was found in the FTP Backup on the ADM. (critical 9.2)
- [CVE-2026-24932](https://insights.sbomify.com/CVE-2026-24932/): An improper certificate validation vulnerability was found in ADM while updating the DDNS settings. (high 8.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6643 and fix it if it is affected.

What it is: CVE-2026-6643 is a high-severity memory corruption vulnerability in ASUSTOR Inc. ADM, published on 20 Apr 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-6643 in the wild and no public exploit code.

Affected product: ASUSTOR Inc. ADM. 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-2026-6643/ (Markdown: https://insights.sbomify.com/CVE-2026-6643/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6643
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6643
- OSV: https://osv.dev/vulnerability/CVE-2026-6643

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6643/
Summaries are generated and may contain mistakes; the official description above is the record.