# CVE-2021-34699: Cisco IOS and IOS XE Software TrustSec CLI Parser Denial of Service Vulnerability

> An authenticated remote attacker can cause a Cisco IOS device to reload by requesting a specific CLI command via the web UI, resulting in a denial of service.

- **Severity:** High 7.7 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H`)
- **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 Sep 2021
- **Updated:** 18 Nov 2024
- **Also known as:** GHSA-6q78-w5mw-hqpj

## What is CVE-2021-34699?

CVE-2021-34699 is a high-severity denial of service vulnerability in Cisco Ios, published on 23 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A vulnerability in the TrustSec CLI parser of Cisco IOS and Cisco IOS XE Software could allow an authenticated, remote attacker to cause an affected device to reload. This vulnerability is due to an improper interaction between the web UI and the CLI parser. An attacker could exploit this vulnerability by requesting a particular CLI command to be run through the web UI. A successful exploit could allow the attacker to cause the device to reload, resulting in a denial of service (DoS) condition.

Weakness: CWE-436 (Interpretation Conflict), CWE-435 (Improper Interaction Between Multiple Correctly-Behaving Entities)

## Which versions are affected by CVE-2021-34699?

It affects 2 products.


Products: Cisco Ios, Cisco Ios Xe.

## How do I fix CVE-2021-34699?

No fix has been published for CVE-2021-34699 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-34699 being exploited?

There is no known exploitation of CVE-2021-34699 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Ios

- [CVE-2017-12240](https://insights.sbomify.com/CVE-2017-12240/): Cisco IOS and IOS XE Software DHCP Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2017-3881](https://insights.sbomify.com/CVE-2017-3881/): Cisco IOS and IOS XE Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2018-0167](https://insights.sbomify.com/CVE-2018-0167/): Cisco IOS, XR, and XE Software Buffer Overflow (high 8.8, exploited in the wild)
- [CVE-2017-6736](https://insights.sbomify.com/CVE-2017-6736/): Cisco IOS and IOS XE Software SNMP Remote Code Execution (high 8.8, exploited in the wild)
- [CVE-2017-6737](https://insights.sbomify.com/CVE-2017-6737/): Cisco IOS and IOS XE Software SNMP Remote Code Execution (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-34699 and fix it if it is affected.

What it is: CVE-2021-34699 is a high-severity denial of service vulnerability in Cisco Ios, published on 23 Sep 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-34699 in the wild and no public exploit code.

Affected product: Cisco Ios. 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-2021-34699/ (Markdown: https://insights.sbomify.com/CVE-2021-34699/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34699
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34699
- OSV: https://osv.dev/vulnerability/CVE-2021-34699

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-34699/
Summaries are generated and may contain mistakes; the official description above is the record.