# CVE-2021-1389: Cisco IOS XR and Cisco NX-OS Software IPv6 Access Control List Bypass Vulnerability

> Remote attackers can bypass IPv6 access control lists on Cisco IOS XR and NX-OS devices by sending crafted packets, accessing protected resources.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N`)
- **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 2021
- **Updated:** 8 Nov 2024
- **Also known as:** GHSA-r95g-ccc3-r2m4

## What is CVE-2021-1389?

CVE-2021-1389 is a medium-severity vulnerability in Cisco Ios Xr, published on 4 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 IPv6 traffic processing of Cisco IOS XR Software and Cisco NX-OS Software for certain Cisco devices could allow an unauthenticated, remote attacker to bypass an IPv6 access control list (ACL) that is configured for an interface of an affected device. The vulnerability is due to improper processing of IPv6 traffic that is sent through an affected device. An attacker could exploit this vulnerability by sending crafted IPv6 packets that traverse the affected device. A successful exploit could allow the attacker to access resources that would typically be protected by the interface ACL.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2021-1389?

It affects 2 products.


Products: Cisco Ios Xr, Cisco Nx-Os.

## How do I fix CVE-2021-1389?

No fix has been published for CVE-2021-1389 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-1389 being exploited?

There is no known exploitation of CVE-2021-1389 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Ios Xr

- [CVE-2020-3118](https://insights.sbomify.com/CVE-2020-3118/): Cisco IOS XR Software Discovery Protocol Format String (high 8.8, exploited in the wild)
- [CVE-2020-3569](https://insights.sbomify.com/CVE-2020-3569/): Cisco IOS XR Software DVMRP Memory Exhaustion (high 8.6, exploited in the wild)
- [CVE-2020-3566](https://insights.sbomify.com/CVE-2020-3566/): Cisco IOS XR Software DVMRP Memory Exhaustion (high 8.6, exploited in the wild)
- [CVE-2010-3035](https://insights.sbomify.com/CVE-2010-3035/): Cisco IOS XR Border Gateway Protocol (BGP) Denial-of-Service (high 7.5, exploited in the wild)
- [CVE-2022-20821](https://insights.sbomify.com/CVE-2022-20821/): Cisco IOS XR Open Port (medium 6.5, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-1389 and fix it if it is affected.

What it is: CVE-2021-1389 is a medium-severity vulnerability in Cisco Ios Xr, published on 4 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-2021-1389 in the wild and no public exploit code.

Affected product: Cisco Ios Xr. 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-2021-1389/ (Markdown: https://insights.sbomify.com/CVE-2021-1389/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-1389
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-1389
- OSV: https://osv.dev/vulnerability/CVE-2021-1389

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-1389/
Summaries are generated and may contain mistakes; the official description above is the record.