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JunosOperating system · Juniper

CVE-2024-21603

MEDIUM · 6.5 CVSS v3.1 Published 2024-01-12
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable 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 the kernel of Juniper Network Junos OS on MX Series allows a network based attacker with low privileges to cause a denial of service. If a scaled configuration for Source class usage (SCU) / destination class usage (DCU) (more than 10 route classes) is present and the SCU/DCU statistics are gathered by executing specific SNMP requests or CLI commands, a 'vmcore' for the RE kernel will be seen which leads to a device restart. Continued exploitation of this issue will lead to a sustained DoS. This issue only affects MX Series devices with MPC10, MPC11 or LC9600, and MX304. No other MX Series devices are affected. This issue affects Juniper Networks Junos OS: * All versions earlier than 20.4R3-S9; * 21.2 versions earlier than 21.2R3-S6; * 21.3 versions earlier than 21.3R3-S5; * 21.4 versions earlier than 21.4R3; * 22.1 versions earlier than 22.1R3; * 22.2 versions earlier than 22.2R2; * 22.3 versions earlier than 22.3R2.

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

Improper check for unusual conditions in Junos OS kernel on MX Series allows low-privileged network attacker to trigger RE kernel vmcore and device restart when scaled SCU/DCU configuration (>10 route classes) is present and specific SNMP requests or CLI commands trigger statistics gathering. Only affects MPC10, MPC11, LC9600, and MX304 hardware.

MitigationApply Junos OS updates per version matrix; for affected devices with scaled SCU/DCU config, consider restricting SNMP access and CLI permissions until patch deployment.

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= 21.2= 21.3= 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
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/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 hardware model
    Run 'show chassis hardware' or 'show hardware' to confirm the device is an MX Series and identify the specific line card or hardware: MPC10, MPC11, LC9600, or MX304.
    Affected if Hardware is MX Series with MPC10, MPC11, LC9600, or MX304 line cards.
  2. Check Junos OS version
    Run 'show version' to obtain the installed Junos OS version.
    Affected if Version is 20.4, 21.2, 21.3, 21.4, 22.1, 22.2, or 22.3.
  3. Verify SCU/DCU configuration
    Run 'show configuration | match "source-class|dest-class"' and count the number of unique route classes configured. Look for SCU (Source Class Usage) and DCU (Destination Class Usage) configurations.
    Affected if Scaled SCU/DCU configuration exists with more than 10 route classes defined.
  4. Check SNMP configuration
    Run 'show configuration snmp' to see if SNMP is enabled and what communities or views are configured.
    Affected if SNMP is enabled and accessible to low-privileged network attackers.
  5. Inspect for recent vmcore events
    Run 'show system core-dumps' or check /var/crash/ for recent vmcore files. Run 'show system reboot history' to look for unexpected restarts.
    Affected if Recent vmcore dumps or unexplained device restarts are present on the system.

The device is affected if it is an MX Series with MPC10/MPC11/LC9600/MX304 hardware, runs an affected Junos version (20.4, 21.2-22.3), has scaled SCU/DCU configuration with >10 route classes, and has exposed SNMP access or CLI permissions that could trigger the statistics gathering that causes the RE kernel vmcore and restart.

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 Junos OS updates per version matrix; for affected devices with scaled SCU/DCU config, consider restricting SNMP access and CLI permissions until patch deployment.

Recommended fix High confidence

Upgrade to 20.4R3-S9 / 21.2R3-S6 / 21.3R3-S5 / 21.4R3 / 22.1R3 / 22.2R2 / 22.3R2 or later (choose based on current version branch)

  1. 1. Identify the current Junos OS version on the MX Series device using 'show version' command
  2. 2. Determine the appropriate upgrade path based on current version (20.4 -> 20.4R3-S9, 21.2 -> 21.2R3-S6, 21.3 -> 21.3R3-S5, 21.4 -> 21.4R3, 22.1 -> 22.1R3, 22.2 -> 22.2R2, 22.3 -> 22.3R2)
  3. 3. Verify the device hardware is MPC10, MPC11, LC9600, or MX304 as only these are affected
  4. 4. Confirm the device has SCU/DCU configuration with more than 10 route classes using 'show configuration | match class'
  5. 5. Download the appropriate fixed Junos OS release from Juniper support portal
  6. 6. Upload the image to the device and verify integrity using 'request system software validate <image>'
  7. 7. Install the upgrade using 'request system software add <image> reboot'
  8. 8. After reboot, verify the new version with 'show version'
Caveat Standard Junos upgrade precautions apply - validate configuration compatibility and have rollback plan

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

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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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-2024-21603 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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