# CVE-2020-1639: Denial of service in Junos OS

> An attacker can cause a denial of service by sending crafted Ethernet OAM packets that crash the CFM daemon on Juniper Junos OS devices.

- **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:** 8 Apr 2020
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-rvxm-fxrp-q47c

## What is CVE-2020-1639?

CVE-2020-1639 is a high-severity denial of service vulnerability in Juniper Junos, published on 8 Apr 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

When an attacker sends a specific crafted Ethernet Operation, Administration, and Maintenance (Ethernet OAM) packet to a target device, it may improperly handle the incoming malformed data and fail to sanitize this incoming data resulting in an overflow condition. This overflow condition in Juniper Networks Junos OS allows an attacker to cause a Denial of Service (DoS) condition by coring the CFM daemon. Continued receipt of these packets may cause an extended Denial of Service condition. This issue affects: Juniper Networks Junos OS 12.3 versions prior to 12.3R12-S15; 12.3X48 versions prior to 12.3X48-D95 on SRX Series; 14.1X50 versions prior to 14.1X50-D145; 14.1X53 versions prior to 14.1X53-D47; 15.1 versions prior to 15.1R2; 15.1X49 versions prior to 15.1X49-D170 on SRX Series; 15.1X53 versions prior to 15.1X53-D67.

Weakness: CWE-755 (Improper Handling of Exceptional Conditions), CWE-703 (Improper Check or Handling of Exceptional Conditions)

## Which versions are affected by CVE-2020-1639?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2020-1639?

No fix has been published for CVE-2020-1639 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-1639 being exploited?

There is no known exploitation of CVE-2020-1639 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-2020-1639 and fix it if it is affected.

What it is: CVE-2020-1639 is a high-severity denial of service vulnerability in Juniper Junos, published on 8 Apr 2020. 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-2020-1639 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-2020-1639/ (Markdown: https://insights.sbomify.com/CVE-2020-1639/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-1639
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-1639
- OSV: https://osv.dev/vulnerability/CVE-2020-1639

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-1639/
Summaries are generated and may contain mistakes; the official description above is the record.