# CVE-2021-1268: Cisco IOS XR Software IPv6 Flood Denial of Service Vulnerability

> An adjacent attacker can cause a denial of service on Cisco IOS XR management interfaces by injecting specific IPv6 multicast packets.

- **Severity:** High 7.4 (`CVSS:3.1/AV:A/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:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 4 Feb 2021
- **Updated:** 8 Nov 2024
- **Also known as:** GHSA-374q-g769-jjp8

## What is CVE-2021-1268?

CVE-2021-1268 is a high-severity denial of service vulnerability in Cisco Ios Xr, published on 4 Feb 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A vulnerability in the IPv6 protocol handling of the management interfaces of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause an IPv6 flood on the management interface network of an affected device. The vulnerability exists because the software incorrectly forwards IPv6 packets that have an IPv6 node-local multicast group address destination and are received on the management interfaces. An attacker could exploit this vulnerability by connecting to the same network as the management interfaces and injecting IPv6 packets that have an IPv6 node-local multicast group address destination. A successful exploit could allow the attacker to cause an IPv6 flood on the corresponding network. Depending on the number of Cisco IOS XR Software nodes on that network segment, exploitation could cause excessive network traffic, resulting in network degradation or a denial of service (DoS) condition.

Weakness: CWE-1076 (Insufficient Adherence to Expected Conventions)

## Which versions are affected by CVE-2021-1268?

It affects 1 product.


Products: Cisco Ios Xr.

## How do I fix CVE-2021-1268?

No fix has been published for CVE-2021-1268 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-1268 being exploited?

There is no known exploitation of CVE-2021-1268 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-2021-1268 and fix it if it is affected.

What it is: CVE-2021-1268 is a high-severity denial of service vulnerability in Cisco Ios Xr, published on 4 Feb 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-1268 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-2021-1268/ (Markdown: https://insights.sbomify.com/CVE-2021-1268/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-1268
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-1268
- OSV: https://osv.dev/vulnerability/CVE-2021-1268

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-1268/
Summaries are generated and may contain mistakes; the official description above is the record.