# CVE-2021-0285: Denial of service in Junos OS

> Attackers can cause sustained denial of service on Juniper switches by flooding traffic, disrupting MC-LAG control connections and causing traffic loss.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Jul 2021
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-xw36-22jx-j7vq

## What is CVE-2021-0285?

CVE-2021-0285 is a high-severity denial of service vulnerability in Juniper Junos, published on 15 Jul 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An uncontrolled resource consumption vulnerability in Juniper Networks Junos OS on QFX5000 Series and EX4600 Series switches allows an attacker sending large amounts of legitimate traffic destined to the device to cause Interchassis Control Protocol (ICCP) interruptions, leading to an unstable control connection between the Multi-Chassis Link Aggregation Group (MC-LAG) nodes which can in turn lead to traffic loss. Continued receipt of this amount of traffic will create a sustained Denial of Service (DoS) condition. An indication that the system could be impacted by this issue is the following log message: "DDOS_PROTOCOL_VIOLATION_SET: Warning: Host-bound traffic for protocol/exception LOCALNH:aggregate exceeded its allowed bandwidth at fpc <fpc number> for <n> times, started at <timestamp>" This issue affects Juniper Networks Junos OS on QFX5000 Series and EX4600 Series: 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R2-S13, 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R2-S8, 18.4R3-S7; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R1-S6, 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R2-S4, 19.4R3-S2; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R2-S3, 20.2R3; 20.3 versions prior to 20.3R2; 20.4 versions prior to 20.4R1-S1, 20.4R2.

Weakness: CWE-400 (Uncontrolled Resource Consumption), CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2021-0285?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2021-0285?

No fix has been published for CVE-2021-0285 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-0285 being exploited?

There is no known exploitation of CVE-2021-0285 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-2021-0285 and fix it if it is affected.

What it is: CVE-2021-0285 is a high-severity denial of service vulnerability in Juniper Junos, published on 15 Jul 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-2021-0285 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-2021-0285/ (Markdown: https://insights.sbomify.com/CVE-2021-0285/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-0285
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-0285
- OSV: https://osv.dev/vulnerability/CVE-2021-0285

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-0285/
Summaries are generated and may contain mistakes; the official description above is the record.