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JunosOperating system · Juniper

CVE-2021-0202

HIGH · 7.5 CVSS v3.1 Published 2021-01-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable 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
On Juniper Networks MX Series and EX9200 Series platforms with Trio-based MPC (Modular Port Concentrator) where Integrated Routing and Bridging (IRB) interface is configured and it is mapped to a VPLS instance or a Bridge-Domain, certain network events at Customer Edge (CE) device may cause memory leak in the MPC which can cause an out of memory and MPC restarts. When this issue occurs, there will be temporary traffic interruption until the MPC is restored. An administrator can use the following CLI command to monitor the status of memory usage level of the MPC: user@device> show system resource-monitor fpc FPC Resource Usage Summary Free Heap Mem Watermark : 20 % Free NH Mem Watermark : 20 % Free Filter Mem Watermark : 20 % * - Watermark reached Slot # % Heap Free RTT Average RTT 1 87 PFE # % ENCAP mem Free % NH mem Free % FW mem Free 0 NA 88 99 1 NA 89 99 When the issue is occurring, the value of “% NH mem Free” will go down until the MPC restarts. This issue affects MX Series and EX9200 Series with Trio-based PFEs (Packet Forwarding Engines). Please refer to https://kb.juniper.net/KB25385 for the list of Trio-based PFEs. This issue affects Juniper Networks Junos OS on MX Series, EX9200 Series: 17.3R3-S8; 17.4R3-S2; 18.2R3-S4, 18.2R3-S5; 18.3R3-S2, 18.3R3-S3; 18.4 versions starting from 18.4R3-S1 and later versions prior to 18.4R3-S6; 19.2 versions starting from 19.2R2 and later versions prior to 19.2R3-S1; 19.4 versions starting from 19.4R2 and later versions prior to 19.4R2-S3, 19.4R3; 20.2 versions starting from 20.2R1 and later versions prior to 20.2R1-S3, 20.2R2. This issue does not affect Juniper Networks Junos OS: 18.1, 19.1, 19.3, 20.1.

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 memory leak vulnerability exists in Juniper MX Series and EX9200 Series platforms with Trio-based MPCs when an IRB interface is mapped to a VPLS instance or Bridge-Domain. Certain network events at the CE device trigger memory exhaustion in the Packet Forwarding Engine, specifically consuming NH (Next-Hop) memory until the MPC restarts due to out-of-memory conditions, causing traffic interruption.

MitigationUpgrade Junos OS to a fixed version (18.4R3-S6, 19.2R3-S1, 19.4R2-S3, 19.4R3, 20.2R1-S3, or 20.2R2+). Monitor FPC memory using 'show system resource-monitor fpc' and watch for decreasing '% NH mem Free' values indicating the leak.

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:= 17.3= 17.4= 18.2= 18.3= 18.4= 19.2= 19.4= 20.2

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

CVSS:3.1/AV:N/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. Confirm device model is affected
    Run 'show chassis hardware' or 'show version' to verify the device is a Juniper MX Series or EX9200 Series with Trio-based MPCs
    Affected if Device is MX Series or EX9200 with Trio-based MPCs installed
  2. Check Junos OS version
    Run 'show version' to obtain the installed Junos OS version
    Affected if Version matches 17.3, 17.4, 18.2, 18.3, 18.4, 19.2, 19.4, or 20.2
  3. Verify IRB interface configuration
    Run 'show configuration interfaces irb' and 'show configuration routing-instances' to check if any IRB interface is mapped to a VPLS instance or Bridge-Domain
    Affected if An IRB interface is configured with instance-type vpls or bridge-domain
  4. Monitor NH memory usage
    Run 'show system resource-monitor fpc' and examine the '% NH mem Free' column for each FPC
    Affected if NH memory free percentage is decreasing over time or shows abnormally low values indicating a leak

Device is affected if it is an MX Series or EX9200 with Trio MPCs, runs a vulnerable Junos version, has an IRB interface mapped to VPLS or Bridge-Domain, and shows decreasing NH memory free percentage.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Junos OS to a fixed version (18.4R3-S6, 19.2R3-S1, 19.4R2-S3, 19.4R3, 20.2R1-S3, or 20.2R2+). Monitor FPC memory using 'show system resource-monitor fpc' and watch for decreasing '% NH mem Free' values indicating the leak.

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation3.0 h
  • Testing4.0 h
  • Review / QA2.0 h
13.0 hours of engineering $2,300
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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-2021-0202 in production — separate from our analysis above.

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What this is

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