# CVE-2021-1387: Cisco NX-OS Software IPv6 Netstack Denial of Service Vulnerability

> Unauthenticated remote attackers can cause a denial of service on Cisco NX-OS devices by sending crafted IPv6 packets that exhaust network stack buffers.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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:** 24 Feb 2021
- **Updated:** 8 Nov 2024
- **Also known as:** GHSA-78w3-6j2r-h8rq

## What is CVE-2021-1387?

CVE-2021-1387 is a high-severity denial of service vulnerability in Cisco Nx-Os, published on 24 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the network stack of Cisco NX-OS Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability exists because the software improperly releases resources when it processes certain IPv6 packets that are destined to an affected device. An attacker could exploit this vulnerability by sending multiple crafted IPv6 packets to an affected device. A successful exploit could cause the network stack to run out of available buffers, impairing operations of control plane and management plane protocols and resulting in a DoS condition. Manual intervention would be required to restore normal operations on the affected device. For more information about the impact of this vulnerability, see the Details section of this advisory.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2021-1387?

It affects 2 products.


Products: Cisco Nx-Os, Cisco Unified Computing System.

## How do I fix CVE-2021-1387?

No fix has been published for CVE-2021-1387 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-1387 being exploited?

There is no known exploitation of CVE-2021-1387 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Nx-Os

- [CVE-2024-20399](https://insights.sbomify.com/CVE-2024-20399/): Cisco NX-OS Command Injection (medium 6.0, exploited in the wild)
- [CVE-2021-1361](https://insights.sbomify.com/CVE-2021-1361/): Cisco NX-OS Software Unauthenticated Arbitrary File Actions Vulnerability (critical 9.8)
- [CVE-2018-0301](https://insights.sbomify.com/CVE-2018-0301/): Memory corruption in Cisco NX-OS unknown (critical 9.8)
- [CVE-2016-1453](https://insights.sbomify.com/CVE-2016-1453/): Memory corruption in n/a (critical 9.8)
- [CVE-2016-1341](https://insights.sbomify.com/CVE-2016-1341/): Hardcoded credentials in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-1387 and fix it if it is affected.

What it is: CVE-2021-1387 is a high-severity denial of service vulnerability in Cisco Nx-Os, published on 24 Feb 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-2021-1387 in the wild and no public exploit code.

Affected product: Cisco Nx-Os. 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-2021-1387/ (Markdown: https://insights.sbomify.com/CVE-2021-1387/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-1387
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-1387
- OSV: https://osv.dev/vulnerability/CVE-2021-1387

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-1387/
Summaries are generated and may contain mistakes; the official description above is the record.