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JunosOperating system · Juniper

CVE-2023-36842

MEDIUM · 6.5 CVSS v3.1 Published 2024-01-12
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 Check for Unusual or Exceptional Conditions vulnerability in Juniper DHCP Daemon (jdhcpd) of Juniper Networks Junos OS allows an adjacent, unauthenticated attacker to cause the jdhcpd to consume all the CPU cycles resulting in a Denial of Service (DoS). On Junos OS devices with forward-snooped-client configured, if an attacker sends a specific DHCP packet to a non-configured interface, this will cause an infinite loop. The DHCP process will have to be restarted to recover the service. This issue affects: Juniper Networks Junos OS * All versions earlier than 20.4R3-S9; * 21.2 versions earlier than 21.2R3-S7; * 21.3 versions earlier than 21.3R3-S5; * 21.4 versions earlier than 21.4R3-S5; * 22.1 versions earlier than 22.1R3-S4; * 22.2 versions earlier than 22.2R3-S3; * 22.3 versions earlier than 22.3R3-S2; * 22.4 versions earlier than 22.4R2-S2, 22.4R3; * 23.2 versions earlier than 23.2R2.

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 Juniper's DHCP daemon (jdhcpd) exists where improper handling of exceptional conditions causes an infinite loop when specific DHCP packets are sent to non-configured interfaces on devices with forward-snooped-client enabled, resulting in CPU exhaustion and denial of service.

MitigationApply the vendor-supplied Junos OS patches for the specific versions listed in the advisory; ensure forward-snooped-client configurations are reviewed and devices are updated to a fixed release.

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= 21.2= 21.3= 21.4= 22.1= 22.2= 22.3= 22.4= 23.2

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. Verify Junos version is affected
    Run 'show version' to identify the installed Junos OS version. Compare against affected versions: any version < 20.4, or exactly 20.4, 21.2, 21.3, 21.4, 22.1, 22.2, 22.3, 22.4, or 23.2
    Affected if Installed Junos version matches any of the listed affected versions
  2. Confirm forward-snooped-client is enabled
    Run 'show configuration | display set | match forward-snooped-client' to check if the DHCP snooping feature forward-snooped-client is configured
    Affected if The forward-snooped-client configuration option is present in the device configuration
  3. Identify DHCP interfaces
    Run 'show dhcp interface' to list all interfaces configured for DHCP and identify any that may be partially configured or lack complete DHCP settings
    Affected if There are DHCP interfaces configured, particularly non-configured or partially configured ones, that could receive DHCP packets

Device is affected only if running an affected Junos version AND has forward-snooped-client enabled AND has DHCP interfaces present that could receive packets on non-configured interfaces

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

Apply the vendor-supplied Junos OS patches for the specific versions listed in the advisory; ensure forward-snooped-client configurations are reviewed and devices are updated to a fixed release.

Recommended fix High confidence

20.4R3-S9, 21.2R3-S7, 21.3R3-S5, 21.4R3-S5, 22.1R3-S4, 22.2R3-S3, 22.3R3-S2, 22.4R2-S2, 22.4R3, or 23.2R2 depending on your branch

  1. Identify the current Junos OS version using "show version" command
  2. Determine the appropriate upgrade path based on current version branch (20.4, 21.2, 21.3, 21.4, 22.1, 22.2, 22.3, 22.4, or 23.2)
  3. Download the corresponding fixed release from Juniper support portal: 20.4R3-S9, 21.2R3-S7, 21.3R3-S5, 21.4R3-S5, 22.1R3-S4, 22.2R3-S3, 22.3R3-S2, 22.4R2-S2, 22.4R3, or 23.2R2
  4. Upload the upgrade package to the device using "file copy" or USB
  5. Initiate upgrade with "request system software add <package>"
  6. Reboot the device after upgrade completes using "request system reboot"
  7. Verify the jdhcpd process is running normally with "show system processes | match jdhcpd"
  8. Confirm the new version is installed with "show version"
Caveat Standard Junos upgrade risks apply - review release notes for any compatibility concerns, and schedule maintenance window as upgrade will require 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
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
Get the upgrade done

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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-2023-36842 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