# CVE-2018-0056: MX Series: L2ALD daemon may crash if a duplicate MAC is learned by two different interfaces

> A duplicate MAC address on two interfaces can crash the L2ALD daemon on Juniper MX Series devices configured with l2-backhaul VPN.

- **Severity:** Medium 6.5 (`CVSS:3.0/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:** 10 Oct 2018
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-3m6q-v5hr-w29h

## What is CVE-2018-0056?

CVE-2018-0056 is a medium-severity denial of service vulnerability in Juniper Junos, published on 10 Oct 2018. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

If a duplicate MAC address is learned by two different interfaces on an MX Series device, the MAC address learning function correctly flaps between the interfaces. However, the Layer 2 Address Learning Daemon (L2ALD) daemon might crash when attempting to delete the duplicate MAC address when the particular entry is not found in the internal MAC address table. This issue only occurs on MX Series devices with l2-backhaul VPN configured. No other products or platforms are affected by this issue. Affected releases are Juniper Networks Junos OS: 15.1 versions prior to 15.1R7-S1 on MX Series; 16.1 versions prior to 16.1R4-S12, 16.1R6-S6 on MX Series; 16.2 versions prior to 16.2R2-S7 on MX Series; 17.1 versions prior to 17.1R2-S9 on MX Series; 17.2 versions prior to 17.2R1-S7, 17.2R2-S6 on MX Series; 17.3 versions prior to 17.3R2-S4, 17.3R3-S1 on MX Series; 17.4 versions prior to 17.4R1-S5 on MX Series; 18.1 versions prior to 18.1R2 on MX Series.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2018-0056?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2018-0056?

No fix has been published for CVE-2018-0056 yet. Limit exposure of the affected software until one is available.

## Is CVE-2018-0056 being exploited?

There is no known exploitation of CVE-2018-0056 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-2018-0056 and fix it if it is affected.

What it is: CVE-2018-0056 is a medium-severity denial of service vulnerability in Juniper Junos, published on 10 Oct 2018. 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-2018-0056 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-2018-0056/ (Markdown: https://insights.sbomify.com/CVE-2018-0056/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-0056
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-0056
- OSV: https://osv.dev/vulnerability/CVE-2018-0056

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-0056/
Summaries are generated and may contain mistakes; the official description above is the record.