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JunosOperating system · Juniper

CVE-2018-0056

MEDIUM · 5.3 CVSS v3.0 Published 2018-10-10
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
58/100
Remediation priority · Elevated
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

On MX Series devices with l2-backhaul VPN configured, the L2ALD (Layer 2 Address Learning Daemon) crashes when attempting to delete a duplicate MAC address that was learned on two different interfaces, but the entry is not found in the internal MAC address table. This is a denial-of-service vulnerability causing daemon crash.

MitigationApply the vendor-supplied Junos OS patch/upgrade to the specified fixed versions for your release train. As a workaround, monitor for duplicate MAC addresses and avoid triggering the specific condition until patching is possible.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JunosOperating system
Affected:= 15.1= 16.1= 16.2= 17.1= 17.2= 17.3= 17.4= 18.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.0/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify device model
    Run 'show chassis hardware' or 'show version' to confirm the device is an MX Series router
    Affected if Device is not an MX Series device (the vulnerability only affects MX Series)
  2. Check Junos version
    Run 'show version' to obtain the installed Junos version
    Affected if Version is 15.1, 16.1, 16.2, 17.1, 17.2, 17.3, 17.4, or 18.1 (exact version match required per CVE)
  3. Verify l2-backhaul VPN configuration
    Run 'show configuration | match l2-backhaul' or inspect the configuration under 'logical-systems' or 'routing-instances' for l2-backhaul VPN settings
    Affected if l2-backhaul VPN is not configured (the vulnerability requires l2-backhaul VPN to be enabled)
  4. Check for L2ALD crash events
    Run 'show log messages' or 'show system core-dumps' looking for L2ALD crash indicators, or use 'show system processes l2ald' to check daemon status
    Affected if L2ALD daemon has crashed or shows recent restart events, especially when duplicate MAC addresses are present

Device is affected if it is an MX Series router running Junos 15.1-18.1 with l2-backhaul VPN configured, and duplicate MAC addresses learned on different interfaces trigger the L2ALD crash condition.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor-supplied Junos OS patch/upgrade to the specified fixed versions for your release train. As a workaround, monitor for duplicate MAC addresses and avoid triggering the specific condition until patching is possible.

Fix this in Junos Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,900
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2018-0056 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data