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JunosOperating system · Juniper

CVE-2023-36849

MEDIUM · 6.5 CVSS v3.1 Published 2023-07-14
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
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 Check or Handling of Exceptional Conditions vulnerability in the Layer-2 control protocols daemon (l2cpd) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated adjacent attacker to cause a Denial of Service (DoS). When a malformed LLDP packet is received, l2cpd will crash and restart. 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. Continued receipt of such packets will lead to a sustained Denial of Service. This issue affects: Juniper Networks Junos OS 21.4 versions prior to 21.4R3-S3; 22.1 versions prior to 22.1R3-S3; 22.2 versions prior to 22.2R2-S1, 22.2R3; 22.3 versions prior to 22.3R2. Juniper Networks Junos OS Evolved 21.4-EVO versions prior to 21.4R3-S2-EVO; 22.1-EVO versions prior to 22.1R3-S3-EVO; 22.2-EVO versions prior to 22.2R2-S1-EVO, 22.2R3-EVO; 22.3-EVO versions prior to 22.3R2-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

The l2cpd (Layer-2 control protocols daemon) in Juniper Junos OS and Junos OS Evolved fails to properly handle malformed LLDP packets, causing an unhandled exception that crashes the daemon. When l2cpd restarts, it reinitializes STP protocols (RSTP, MSTP, VSTP), MVRP, ERP, and disrupts LLDP-dependent services like PoE and VoIP. An unauthenticated adjacent attacker on the same network segment can send malformed LLDP packets to trigger repeated crashes, creating a sustained DoS condition.

MitigationApply the vendor-supplied software updates: upgrade to Junos OS 21.4R3-S3, 22.1R3-S3, 22.2R2-S1/22.2R3, 22.3R2 or later (or respective EVO versions). If immediate patching is not feasible, consider network segmentation to limit adjacent attacker access to LLDP-enabled interfaces.

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:= 21.4= 22.1= 22.2= 22.3
Junos Os EvolvedOperating system
Affected:= 21.4= 22.1= 22.2= 22.3

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 identify the installed Junos version
    Affected if The version listed is 21.4, 22.1, 22.2, or 22.3 (any build)
  2. Verify l2cpd daemon is running
    Run `show l2cpd status` or `show system processes | match l2cpd` to confirm the l2cpd daemon is active
    Affected if The l2cpd process is running or attempting to run on the device
  3. Confirm LLDP is enabled
    Run `show lldp interface` or `show lldp neighbors` to check if LLDP is configured on any interface
    Affected if LLDP is enabled on one or more interfaces (this is the vulnerable attack surface)
  4. Check for l2cpd crash logs
    Review system logs with `show log messages | match l2cpd` or `show system core-dumps` for recent l2cpd restarts or crash indications
    Affected if Recent l2cpd restarts, exceptions, or core dumps are present in logs
  5. Verify affected L2 services are disrupted
    Run `show protocols mstp`, `show protocols rstp`, `show protocols vstp`, `show protocols mvrp`, or `show protocols erp` to check for protocol state changes or instability
    Affected if Any of these Layer-2 protocols show unexpected state changes or are not converging properly since a potential crash event

You are affected if you are running Junos version 21.4, 22.1, 22.2, or 22.3 with LLDP enabled on any interface, and l2cpd is the active daemon managing your Layer-2 protocols.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor-supplied software updates: upgrade to Junos OS 21.4R3-S3, 22.1R3-S3, 22.2R2-S1/22.2R3, 22.3R2 or later (or respective EVO versions). If immediate patching is not feasible, consider network segmentation to limit adjacent attacker access to LLDP-enabled interfaces.

Recommended fix High confidence

Junos OS: 21.4R3-S3, 22.1R3-S3, 22.2R3 or 22.2R2-S1, 22.3R2 | Junos OS Evolved: 21.4R3-S2-EVO, 22.1R3-S3-EVO, 22.2R3-EVO or 22.2R2-S1-EVO, 22.3R2-EVO

  1. 1. Identify the current Junos OS or Junos OS Evolved version running on the device using 'show version' command
  2. 2. Determine the appropriate upgrade path based on current version (21.4 -> 21.4R3-S3, 22.1 -> 22.1R3-S3, 22.2 -> 22.2R3 or 22.2R2-S1, 22.3 -> 22.3R2)
  3. 3. Download the appropriate fixed Junos OS or Junos OS Evolved software image from the Juniper Networks support portal
  4. 4. Upload the software image to the device using 'request system software add' command
  5. 5. Reboot the device using 'request system reboot' command to apply the new software
  6. 6. After reboot, verify the new version is running with 'show version' and confirm l2cpd stability with 'show system processes extensive | match l2cpd'
Caveat Standard Junos upgrade considerations apply - review release notes for compatibility, ensure configuration backup before upgrade, and plan maintenance window as upgrade causes system reboot

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

Fix this in Junos Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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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-2023-36849 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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