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JunosOperating system · Juniper

CVE-2023-36850

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 Validation of Specified Index, Position, or Offset in Input vulnerability in the Connectivity Fault Management(CFM) module of Juniper Networks Junos OS on MX Series(except MPC10, MPC11 and LC9600) allows an adjacent attacker on the local broadcast domain to cause a Denial of Service(DoS). Upon receiving a malformed CFM packet, the MPC crashes. Continued receipt of these packets causes a sustained denial of service. This issue can only be triggered when CFM hasn't been configured. This issue affects: Juniper Networks Junos OS All versions prior to 19.1R3-S10 on MX Series; 19.2 versions prior to 19.2R3-S7 on MX Series; 19.3 versions prior to 19.3R3-S8 on MX Series; 19.4 versions prior to 19.4R3-S12 on MX Series; 20.1 version 20.1R1 and later versions on MX Series; 20.2 versions prior to 20.2R3-S7 on MX Series; 20.3 version 20.3R1 and later versions on MX Series; 20.4 versions prior to 20.4R3-S7 on MX Series; 21.1 versions prior to 21.1R3-S5 on MX Series; 21.2 versions prior to 21.2R3-S4 on MX Series; 21.3 versions prior to 21.3R3-S4 on MX Series; 21.4 versions prior to 21.4R3-S3 on MX Series; 22.1 versions prior to 22.1R3-S2 on MX Series; 22.2 versions prior to 22.2R3 on MX Series; 22.3 versions prior to 22.3R2, 22.3R3 on MX Series; 22.4 versions prior to 22.4R2 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

A vulnerability in the Connectivity Fault Management (CFM) module of Juniper Junos OS on MX Series routers allows an adjacent attacker on the local broadcast domain to send malformed CFM packets that crash the MPC. The crash is triggerable only when CFM has not been configured, and continued attacks cause sustained DoS.

MitigationApply the vendor-supplied Junos OS patches for your specific version (see Juniper advisory). Until patched, monitor for MPC crashes and consider implementing network access controls to limit adjacent attackers.

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:= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3= 20.4= 21.1= 21.2= 21.3= 21.4

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. 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 router - this vulnerability only affects MX Series
  2. Check Junos OS version
    Run 'show version' and compare the installed version number against the affected list: 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3, 20.4, 21.1, 21.2, 21.3, 21.4
    Affected if Version matches exactly one of the listed affected versions
  3. Determine if CFM is configured
    Run 'show protocols oam' or 'show protocols cfm' to check for Connectivity Fault Management configuration
    Affected if CFM is NOT configured - the vulnerability triggers specifically when CFM has not been configured
  4. Check for MPC crash logs
    Run 'show log messages' and search for MPC crash events or DPC/MPC related core dumps using 'show system core-dumps'
    Affected if Recent MPC crashes are present in logs without an obvious other cause
  5. Assess network exposure
    Review interface configurations and network segment access to determine if adjacent attackers on the local broadcast domain could send packets to the device
    Affected if Device is accessible to unauthenticated adjacent attackers on broadcast domain segments used by MX interfaces

You are affected if you run an MX Series router on any of the affected Junos versions (19.1-21.4) with CFM not configured, and an adjacent attacker can reach the device on the local broadcast domain.

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 Junos OS patches for your specific version (see Juniper advisory). Until patched, monitor for MPC crashes and consider implementing network access controls to limit adjacent attackers.

Recommended fix High confidence

Upgrade to 19.1R3-S10 or later (19.1x), 19.2R3-S7 or later (19.2x), 19.3R3-S8 or later (19.3x), or 19.4R3-S12 or later (19.4x) - or a later stable release branch

  1. 1. Identify the current Junos OS version on the MX Series device using 'show version'
  2. 2. Plan an upgrade to one of the fixed versions based on your current branch: for 19.1x branch upgrade to 19.1R3-S10 or later; for 19.2x branch upgrade to 19.2R3-S7 or later; for 19.3x branch upgrade to 19.3R3-S8 or later; for 19.4x branch upgrade to 19.4R3-S12 or later
  3. 3. Download the appropriate Junos OS upgrade package from the Juniper Networks support portal
  4. 4. Upload the upgrade package to the MX Series device
  5. 5. Execute the upgrade using 'request system software add <package>' command
  6. 6. Reboot the device using 'request system reboot' command
  7. 7. After reboot, verify the new version is installed using 'show version'
  8. 8. Confirm the CFM functionality is operational and the device is stable
Caveat Standard Junos OS upgrade considerations apply - review release notes for compatibility with other modules and ensure proper configuration backup before upgrading

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

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation12.0 h
  • Testing6.0 h
  • Review / QA3.0 h
25.0 hours of engineering $4,400
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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-2023-36850 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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