# CVE-2026-71920: DrayTek VigorSwitch Multiple Models NULL Pointer Dereference via formlogout

> Remote authenticated attackers can crash DrayTek VigorSwitch devices via a null pointer dereference in the logout function.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Aug 2026
- **Updated:** 24 Aug 2026
- **Also known as:** GHSA-648m-vmc5-h63x

## What is CVE-2026-71920?

CVE-2026-71920 is a medium-severity vulnerability in DrayTek Corporation VigorSwitch FX2120, published on 24 Aug 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

Multiple DrayTek VigorSwitch models contain a null pointer dereference vulnerability in the formlogout function. The vulnerability is caused by missing checks for an empty or absent Cookie header before string handling. A remote attacker can trigger this vulnerability via a crafted request to crash the service and cause a denial of service. Exploitation requires valid administrative credentials for the device's web management interface.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-71920?


## How do I fix CVE-2026-71920?

No fix has been published for CVE-2026-71920 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-71920 being exploited?

There is no known exploitation of CVE-2026-71920 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-71920 and fix it if it is affected.

What it is: CVE-2026-71920 is a medium-severity vulnerability in DrayTek Corporation VigorSwitch FX2120, published on 24 Aug 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-71920 in the wild and no public exploit code.

Affected product: DrayTek Corporation VigorSwitch FX2120. 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-2026-71920/ (Markdown: https://insights.sbomify.com/CVE-2026-71920/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-71920
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-71920
- OSV: https://osv.dev/vulnerability/CVE-2026-71920

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-71920/
Summaries are generated and may contain mistakes; the official description above is the record.