# CVE-2021-45736: Denial of service in n/a

> Attackers can cause a Denial of Service on TOTOLINK X5000R routers via a stack overflow in the setL2tpServerCfg function.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 4 Feb 2022
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-c3p4-6x5w-74fx

## What is CVE-2021-45736?

CVE-2021-45736 is a high-severity denial of service vulnerability in Totolink X5000r Firmware, published on 4 Feb 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

TOTOLINK X5000R v9.1.0u.6118_B20201102 was discovered to contain a stack overflow in the function setL2tpServerCfg. This vulnerability allows attackers to cause a Denial of Service (DoS) via the eip, sip, server parameters.

## Which versions are affected by CVE-2021-45736?

It affects 1 product.


Products: Totolink X5000r Firmware.

## How do I fix CVE-2021-45736?

No fix has been published for CVE-2021-45736 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-45736 being exploited?

There is no known exploitation of CVE-2021-45736 in the wild and no public exploit code.

## Other vulnerabilities in Totolink X5000r Firmware

- [CVE-2025-70327](https://insights.sbomify.com/CVE-2025-70327/): Command injection in n/a (critical 9.8)
- [CVE-2025-13184](https://insights.sbomify.com/CVE-2025-13184/): Auth bypass in X5000R's (AX1800 router) (critical 9.8)
- [CVE-2024-42737](https://insights.sbomify.com/CVE-2024-42737/): Command injection in n/a (critical 9.8)
- [CVE-2024-42745](https://insights.sbomify.com/CVE-2024-42745/): Command injection in n/a (critical 9.8)
- [CVE-2024-42748](https://insights.sbomify.com/CVE-2024-42748/): Command injection in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-45736 and fix it if it is affected.

What it is: CVE-2021-45736 is a high-severity denial of service vulnerability in Totolink X5000r Firmware, published on 4 Feb 2022. 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-2021-45736 in the wild and no public exploit code.

Affected product: Totolink X5000r Firmware. 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-2021-45736/ (Markdown: https://insights.sbomify.com/CVE-2021-45736/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-45736
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-45736
- OSV: https://osv.dev/vulnerability/CVE-2021-45736

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-45736/
Summaries are generated and may contain mistakes; the official description above is the record.