# CVE-2021-34697: Cisco IOS XE Software Protection Against Distributed Denial of Service Attacks Feature Vulnerability

> Remote attackers can cause denial of service on Cisco IOS XE devices if specific anti-DoS features are configured incorrectly.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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:** 23 Sep 2021
- **Updated:** 7 Nov 2024
- **Also known as:** GHSA-7jmp-v8mh-4f8r

## What is CVE-2021-34697?

CVE-2021-34697 is a medium-severity denial of service vulnerability in Cisco Ios Xe, published on 23 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the Protection Against Distributed Denial of Service Attacks feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to conduct denial of service (DoS) attacks to or through the affected device. This vulnerability is due to incorrect programming of the half-opened connections limit, TCP SYN flood limit, or TCP SYN cookie features when the features are configured in vulnerable releases of Cisco IOS XE Software. An attacker could exploit this vulnerability by attempting to flood traffic to or through the affected device. A successful exploit could allow the attacker to initiate a DoS attack to or through an affected device.

Weakness: CWE-665 (Improper Initialization)

## Which versions are affected by CVE-2021-34697?

It affects 1 product.


Products: Cisco Ios Xe.

## How do I fix CVE-2021-34697?

No fix has been published for CVE-2021-34697 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-34697 being exploited?

There is no known exploitation of CVE-2021-34697 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Ios Xe

- [CVE-2023-20198](https://insights.sbomify.com/CVE-2023-20198/): Cisco IOS XE Web UI Privilege Escalation (critical 10.0, exploited in the wild)
- [CVE-2018-0151](https://insights.sbomify.com/CVE-2018-0151/): Cisco IOS Software and Cisco IOS XE Software Quality of Service Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2023-20273](https://insights.sbomify.com/CVE-2023-20273/): Cisco IOS XE Web UI Command Injection (high 7.2, exploited in the wild)
- [CVE-2025-20188](https://insights.sbomify.com/CVE-2025-20188/): Hardcoded credentials in Cisco IOS XE Software (critical 10.0)
- [CVE-2021-34770](https://insights.sbomify.com/CVE-2021-34770/): Cisco IOS XE Software for Catalyst 9000 Family Wireless Controllers CAPWAP Remote Code Execution Vulnerability (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-34697 and fix it if it is affected.

What it is: CVE-2021-34697 is a medium-severity denial of service vulnerability in Cisco Ios Xe, published on 23 Sep 2021. 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-2021-34697 in the wild and no public exploit code.

Affected product: Cisco Ios Xe. 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-2021-34697/ (Markdown: https://insights.sbomify.com/CVE-2021-34697/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34697
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34697
- OSV: https://osv.dev/vulnerability/CVE-2021-34697

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-34697/
Summaries are generated and may contain mistakes; the official description above is the record.