# CVE-2021-0271: Memory corruption in Junos OS

> An adjacent attacker can cause a denial of service on Juniper EX Series switches by sending crafted ARP packets that trigger a double free in the sfid process.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/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:** 22 Apr 2021
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-pmcr-6r2h-238j

## What is CVE-2021-0271?

CVE-2021-0271 is a medium-severity memory corruption vulnerability in Juniper Junos, published on 22 Apr 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A Double Free vulnerability in the software forwarding interface daemon (sfid) process of Juniper Networks Junos OS allows an adjacently-connected attacker to cause a Denial of Service (DoS) by sending a crafted ARP packet to the device. Continued receipt and processing of the crafted ARP packets will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS on EX2200-C Series, EX3200 Series, EX3300 Series, EX4200 Series, EX4500 Series, EX4550 Series, EX6210 Series, EX8208 Series, EX8216 Series. 12.3 versions prior to 12.3R12-S17; 15.1 versions prior to 15.1R7-S8. This issue only affects the listed Marvell-chipset based EX Series devices. No other products or platforms are affected.

Weakness: CWE-415 (Double Free)

## Which versions are affected by CVE-2021-0271?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2021-0271?

No fix has been published for CVE-2021-0271 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-0271 being exploited?

There is no known exploitation of CVE-2021-0271 in the wild and no public exploit code.

## Other vulnerabilities in Juniper Junos

- [CVE-2023-36845](https://insights.sbomify.com/CVE-2023-36845/): Juniper Junos OS EX Series and SRX Series PHP External Variable Modification (critical 9.8, exploited in the wild)
- [CVE-2020-1631](https://insights.sbomify.com/CVE-2020-1631/): Juniper Junos OS Path Traversal (high 8.8, exploited in the wild)
- [CVE-2025-21590](https://insights.sbomify.com/CVE-2025-21590/): Juniper Junos OS Improper Isolation or Compartmentalization (medium 6.7, exploited in the wild)
- [CVE-2023-36851](https://insights.sbomify.com/CVE-2023-36851/): Juniper Junos OS SRX Series Missing Authentication for Critical Function (medium 5.3, exploited in the wild)
- [CVE-2023-36844](https://insights.sbomify.com/CVE-2023-36844/): Juniper Junos OS EX Series PHP External Variable Modification (medium 5.3, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-0271 and fix it if it is affected.

What it is: CVE-2021-0271 is a medium-severity memory corruption vulnerability in Juniper Junos, published on 22 Apr 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-2021-0271 in the wild and no public exploit code.

Affected product: Juniper Junos. 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-2021-0271/ (Markdown: https://insights.sbomify.com/CVE-2021-0271/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-0271
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-0271
- OSV: https://osv.dev/vulnerability/CVE-2021-0271

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-0271/
Summaries are generated and may contain mistakes; the official description above is the record.