# CVE-2021-1243: Cisco IOS XR Software SNMP Management Plane Protection ACL Bypass Vulnerability

> An unauthenticated remote attacker can bypass SNMP management plane protection ACLs on Cisco IOS XR devices, allowing connections to SNMP ports despite configured deny rules.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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-w6r6-frp2-8r52

## What is CVE-2021-1243?

CVE-2021-1243 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 Local Packet Transport Services (LPTS) programming of the SNMP with the management plane protection feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to allow connections despite the management plane protection that is configured to deny access to the SNMP server of an affected device. This vulnerability is due to incorrect LPTS programming when using SNMP with management plane protection. An attacker could exploit this vulnerability by connecting to an affected device using SNMP. A successful exploit could allow the attacker to connect to the device on the configured SNMP ports. Valid credentials are required to execute any of the SNMP requests.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2021-1243?

It affects 1 product.


Products: Cisco Ios Xr.

## How do I fix CVE-2021-1243?

No fix has been published for CVE-2021-1243 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-1243 being exploited?

There is no known exploitation of CVE-2021-1243 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-2021-1243 and fix it if it is affected.

What it is: CVE-2021-1243 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-2021-1243 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-2021-1243/ (Markdown: https://insights.sbomify.com/CVE-2021-1243/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-1243
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-1243
- OSV: https://osv.dev/vulnerability/CVE-2021-1243

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-1243/
Summaries are generated and may contain mistakes; the official description above is the record.