# CVE-2021-0222: Denial of service in Junos OS

> An attacker can cause a denial of service on Juniper network devices by sending crafted protocol packets that trigger excessive traffic replication.

- **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:** 15 Jan 2021
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-px4x-jp5g-9393

## What is CVE-2021-0222?

CVE-2021-0222 is a high-severity denial of service vulnerability in Juniper Junos, published on 15 Jan 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A vulnerability in Juniper Networks Junos OS allows an attacker to cause a Denial of Service (DoS) to the device by sending certain crafted protocol packets from an adjacent device with invalid payloads to the device. These crafted packets, which should be discarded, are instead replicated and sent to the RE. Over time, a Denial of Service (DoS) occurs. Continued receipt of these crafted protocol packets will cause an extended Denial of Service (DoS) condition, which may cause wider traffic impact due to protocol flapping. An indication of compromise is to check "monitor interface traffic" on the ingress and egress port packet counts. For each ingress packet, two duplicate packets are seen on egress. This issue can be triggered by IPv4 and IPv6 packets. This issue affects all traffic through the device. This issue affects: Juniper Networks Junos OS: 14.1X53 versions prior to 14.1X53-D53 on EX4300, QFX3500, QFX5100, EX4600; 15.1 versions prior to 15.1R7-S6 on EX4300, QFX3500, QFX5100, EX4600; 16.1 versions prior to 16.1R7-S7 on EX4300, QFX5100, EX4600; 17.1 versions prior to 17.1R2-S11 on EX4300, QFX5100, EX4600; 17.1 versions prior to 117.1R3-S2 on EX4300; 17.2 versions prior to 17.2R1-S9 on EX4300; 17.2 versions prior to 17.2R3-S3 on EX4300, QFX5100, EX4600, QFX5110, QFX5200; 17.3 versions prior to 17.3R2-S5, 17.3R3-S7 on EX4300, QFX5100, EX4600, QFX5110, QFX5200; 17.4 versions prior to 17.4R2-S9, 17.4R3 on EX4300, QFX5100, EX4600, QFX5110, QFX5200; 18.1 versions prior to 18.1R3-S9 on EX4300, QFX5100, EX4600, QFX5110, QFX5200, QFX5210, EX2300, EX3400; 18.2 versions prior to 18.2R2-S7 on EX4300; 18.2 versions prior to 18.2R3-S3 on EX4300, QFX5100, EX4600, QFX5110, QFX5200, QFX5210, EX2300, EX3400; 18.3 versions prior to 18.3R2-S3, on EX4300; 18.3 versions prior to 18.3R1-S7, 18.3R3-S1 on EX4300, QFX5100, EX4600, QFX5110, QFX5200, QFX5210, QFX5120, EX4650, EX2300, EX3400; 18.4 versions prior to 18.4R1-S5, 18.4R2-S3, 18.4R3 on EX4300, QFX5100, EX4600, QFX5110, QFX5200, QFX5210, QFX5120, EX4650, EX2300, EX3400; 19.1 versions prior to 19.1R1-S4, 19.1R2-S1, 19.1R3 on EX4300, QFX5100, EX4600, QFX5110, QFX5200, QFX5210, QFX5120, EX4650, EX2300, EX3400; 19.2 versions prior to 19.2R1-S4, 19.2R2 on EX4300; 19.2 versions prior to 19.2R1-S3, 19.2R2 on QFX5100, EX4600, QFX5110, QFX5200, QFX5210, QFX5120, EX4650, EX2300, EX3400; 19.3 versions prior to 19.3R2-S1, 19.3R3 on EX4300; 19.3 versions prior to 19.3R1-S1, 19.3R2, 19.3R3 on QFX5100, EX4600, QFX5110, QFX5200, QFX5210, QFX5120, EX4650, EX2300, EX3400;

Weakness: CWE-16

## Which versions are affected by CVE-2021-0222?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2021-0222?

No fix has been published for CVE-2021-0222 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-0222 being exploited?

There is no known exploitation of CVE-2021-0222 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-2021-0222 and fix it if it is affected.

What it is: CVE-2021-0222 is a high-severity denial of service vulnerability in Juniper Junos, published on 15 Jan 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-2021-0222 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-2021-0222/ (Markdown: https://insights.sbomify.com/CVE-2021-0222/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-0222
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-0222
- OSV: https://osv.dev/vulnerability/CVE-2021-0222

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-0222/
Summaries are generated and may contain mistakes; the official description above is the record.