# CVE-2026-4565: Tenda AC21 SetNetControlList formSetQosBand buffer overflow

> Remote attackers can trigger a buffer overflow in the Tenda AC21 router's QoS settings, potentially leading to code execution or service disruption.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 23 Mar 2026
- **Updated:** 23 Mar 2026
- **Also known as:** GHSA-mcx9-w62j-hjwr

## What is CVE-2026-4565?

CVE-2026-4565 is a high-severity memory corruption vulnerability in Tenda AC21, published on 23 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A vulnerability was detected in Tenda AC21 16.03.08.16. Impacted is the function formSetQosBand of the file /goform/SetNetControlList. Performing a manipulation of the argument list results in buffer overflow. The attack can be initiated remotely. The exploit is now public and may be used.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input), CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2026-4565?

It affects 1 product.


Products: Tenda Ac21 Firmware.

## How do I fix CVE-2026-4565?

No fix has been published for CVE-2026-4565 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-4565 being exploited?

There is no known exploitation of CVE-2026-4565 in the wild and no public exploit code.

## Other vulnerabilities in Tenda AC21

- [CVE-2025-9605](https://insights.sbomify.com/CVE-2025-9605/): Tenda AC21/AC23 GetParentControlInfo stack-based overflow (critical 9.3)
- [CVE-2023-24333](https://insights.sbomify.com/CVE-2023-24333/): Command injection in n/a (high 8.8)
- [CVE-2026-1637](https://insights.sbomify.com/CVE-2026-1637/): Tenda AC21 AdvSetMacMtuWan fromAdvSetMacMtuWan stack-based overflow (high 8.7)
- [CVE-2025-13445](https://insights.sbomify.com/CVE-2025-13445/): Tenda AC21 SetIpMacBind stack-based overflow (high 8.7)
- [CVE-2025-13446](https://insights.sbomify.com/CVE-2025-13446/): Tenda AC21 SetSysTimeCfg stack-based overflow (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-4565 and fix it if it is affected.

What it is: CVE-2026-4565 is a high-severity memory corruption vulnerability in Tenda AC21, published on 23 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-4565 in the wild and no public exploit code.

Affected product: Tenda AC21. 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-2026-4565/ (Markdown: https://insights.sbomify.com/CVE-2026-4565/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4565
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4565
- OSV: https://osv.dev/vulnerability/CVE-2026-4565

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-4565/
Summaries are generated and may contain mistakes; the official description above is the record.