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JunosOperating system · Juniper

CVE-2023-36839

MEDIUM · 6.5 CVSS v3.1 Published 2023-10-12
Fix available
A fix is available. Upgrade to 20.4 or later.
See remediation →
70/100
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
An Improper Validation of Specified Quantity in Input vulnerability in the Layer-2 control protocols daemon (l2cpd) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated adjacent attacker who sends specific LLDP packets to cause a Denial of Service(DoS). This issue occurs when specific LLDP packets are received and telemetry polling is being done on the device. The impact of the l2cpd crash is reinitialization of STP protocols (RSTP, MSTP or VSTP), and MVRP and ERP. Also, if any services depend on LLDP state (like PoE or VoIP device recognition), then these will also be affected. This issue affects: Juniper Networks Junos OS * All versions prior to 20.4R3-S8; * 21.1 version 21.1R1 and later versions; * 21.2 versions prior to 21.2R3-S5; * 21.3 versions prior to 21.3R3-S4; * 21.4 versions prior to 21.4R3-S3; * 22.1 versions prior to 22.1R3-S2; * 22.2 versions prior to 22.2R3; * 22.3 versions prior to 22.3R2-S2; * 22.4 versions prior to 22.4R2; Juniper Networks Junos OS Evolved * All versions prior to 20.4R3-S8-EVO; * 21.1 version 21.1R1-EVO and later versions; * 21.2 versions prior to 21.2R3-S5-EVO; * 21.3 versions prior to 21.3R3-S4-EVO; * 21.4 versions prior to 21.4R3-S3-EVO; * 22.1 versions prior to 22.1R3-S2-EVO; * 22.2 versions prior to 22.2R3-EVO; * 22.3 versions prior to 22.3R2-S2-EVO; * 22.4 versions prior to 22.4R1-S1-EVO;

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

A vulnerability in the Layer-2 control protocols daemon (l2cpd) of Juniper Networks Junos OS allows an unauthenticated adjacent attacker to cause denial of service by sending specifically crafted LLDP packets while telemetry polling is active. The l2cpd crash causes reinitialization of STP protocols (RSTP, MSTP, VSTP), MVRP, ERP, and disrupts services dependent on LLDP state such as PoE and VoIP device recognition.

MitigationUpgrade Junos OS and Junos OS Evolved to the specified patched versions that address this vulnerability. If immediate patching is not possible, consider disabling LLDP on untrusted interfaces or implementing network access control to limit adjacency attacks.

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:< 20.4= 20.4= 21.1= 21.2= 21.3= 21.4= 22.1= 22.2= 22.3= 22.4
Junos Os EvolvedOperating system
Affected:< 20.4= 20.4= 21.1= 21.2= 21.3= 21.4= 22.1= 22.2= 22.3= 22.4

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
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/AC:L/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. Check Junos OS version
    Run 'show version' or 'show version detail' to display the installed Junos OS version
    Affected if The installed version matches one of the affected versions: 20.4, 21.1, 21.2, 21.3, 21.4, 22.1, 22.2, 22.3, 22.4, or any version prior to 20.4
  2. Verify l2cpd daemon is running
    Run 'show system processes extensive | match l2cpd' or check process status via 'show system processes'
    Affected if The l2cpd process is active on the device
  3. Confirm LLDP is enabled
    Run 'show lldp neighbors' or 'show lldp interface' to check LLDP status
    Affected if LLDP is enabled on any interface (the vulnerability is triggered by crafted LLDP packets)
  4. Check if telemetry polling is active
    Run 'show lldp statistics' or check for telemetry-related configuration under 'set protocols lldp' hierarchy
    Affected if Telemetry polling is configured and active (this is required for the exploit to trigger)
  5. Identify affected protocols in use
    Run 'show protocols spanning-tree', 'show protocols mvrp', 'show protocols erp' to check for these protocols
    Affected if Any of RSTP, MSTP, VSTP, MVRP, or ERP protocols are enabled (these will be disrupted if l2cpd crashes)

A user is affected if they are running an affected Junos version with l2cpd running, LLDP enabled, and telemetry polling active, especially if they have STP, MVRP, or ERP protocols configured.

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.

dbcve · scoped
Upgrade available Upgrade to 20.4 or later
Fixed in 20.4
Interim mitigation

Upgrade Junos OS and Junos OS Evolved to the specified patched versions that address this vulnerability. If immediate patching is not possible, consider disabling LLDP on untrusted interfaces or implementing network access control to limit adjacency attacks.

Recommended fix High confidence

Upgrade to the minimum fixed release for your version branch: 20.4R3-S8, 21.1R3-S4, 21.2R3-S5, 21.3R3-S4, 21.4R3-S3, 22.1R3-S2, 22.2R3, 22.3R2-S2, or 22.4R2 (or corresponding -EVO versions for Junos OS Evolved)

  1. 1. Identify the current Junos OS or Junos OS Evolved version running on the device using 'show version'
  2. 2. Based on the installed version branch, plan an upgrade to the minimum fixed release: For 20.4 branch: upgrade to 20.4R3-S8 or later; For 21.1 branch: upgrade to 21.1R3-S4 or later; For 21.2 branch: upgrade to 21.2R3-S5 or later; For 21.3 branch: upgrade to 21.3R3-S4 or later; For 21.4 branch: upgrade to 21.4R3-S3 or later; For 22.1 branch: upgrade to 22.1R3-S2 or later; For 22.2 branch: upgrade
  3. 3. Download the appropriate upgrade package from the Juniper Networks support portal
  4. 4. Upload the upgrade package to the device using 'file copy' or USB
  5. 5. Initiate the upgrade using 'request system software add <package>' command
  6. 6. Reboot the device after upgrade completes using 'request system reboot'
  7. 7. After reboot, verify the new version is running with 'show version' and confirm l2cpd is operational
  8. 8. Verify LLDP functionality is working with 'show lldp' and check for any errors
Caveat Standard Junos upgrade considerations apply - review release notes for any changes to features in use; ensure compatibility with other network devices and review configuration migration requirements

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
13.0 hours of engineering $2,280
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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-2023-36839 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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