# CVE-2018-0021: Junos OS: Short MacSec keys may allow man-in-the-middle attacks.

> Short MacSec keys in Junos OS allow attackers to discover secrets via brute-force, enabling man-in-the-middle attacks.

- **Severity:** High 8.8 (`CVSS:3.0/AV:A/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 11 Apr 2018
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-cm2c-mr99-4v22

## What is CVE-2018-0021?

CVE-2018-0021 is a high-severity vulnerability in Juniper Junos, published on 11 Apr 2018. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

If all 64 digits of the connectivity association name (CKN) key or all 32 digits of the connectivity association key (CAK) key are not configured, all remaining digits will be auto-configured to 0. Hence, Juniper devices configured with short MacSec keys are at risk to an increased likelihood that an attacker will discover the secret passphrases configured for these keys through dictionary-based and brute-force-based attacks using spoofed packets. Affected releases are Juniper Networks Junos OS: 14.1 versions prior to 14.1R10, 14.1R9; 14.1X53 versions prior to 14.1X53-D47; 15.1 versions prior to 15.1R4-S9, 15.1R6-S6, 15.1R7; 15.1X49 versions prior to 15.1X49-D100; 15.1X53 versions prior to 15.1X53-D59; 16.1 versions prior to 16.1R3-S8, 16.1R4-S8, 16.1R5; 16.2 versions prior to 16.2R1-S6, 16.2R2; 17.1 versions prior to 17.1R2.

## Which versions are affected by CVE-2018-0021?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2018-0021?

No fix has been published for CVE-2018-0021 yet. Limit exposure of the affected software until one is available.

## Is CVE-2018-0021 being exploited?

There is no known exploitation of CVE-2018-0021 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-2018-0021 and fix it if it is affected.

What it is: CVE-2018-0021 is a high-severity vulnerability in Juniper Junos, published on 11 Apr 2018. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2018-0021 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-2018-0021/ (Markdown: https://insights.sbomify.com/CVE-2018-0021/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-0021
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-0021
- OSV: https://osv.dev/vulnerability/CVE-2018-0021

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-0021/
Summaries are generated and may contain mistakes; the official description above is the record.