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JunosOperating system · Juniper

CVE-2021-0211

CRITICAL · 10.0 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 →
100/100
Remediation priority · Urgent
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
An improper check for unusual or exceptional conditions in Juniper Networks Junos OS and Junos OS Evolved Routing Protocol Daemon (RPD) service allows an attacker to send a valid BGP FlowSpec message thereby causing an unexpected change in the route advertisements within the BGP FlowSpec domain leading to disruptions in network traffic causing a Denial of Service (DoS) condition. Continued receipt of these update messages will cause a sustained Denial of Service condition. This issue affects Juniper Networks: Junos OS: All versions prior to 17.3R3-S10 with the exceptions of 15.1X49-D240 on SRX Series and 15.1R7-S8 on EX Series; 17.3 versions prior to 17.3R3-S10; 17.4 versions prior to 17.4R2-S12, 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.2 versions prior to 18.2R2-S8, 18.2R3-S6; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S6, 18.4R3-S6; 19.1 versions prior to 19.1R1-S6, 19.1R2-S2, 19.1R3-S3; 19.2 versions prior to 19.2R3-S1; 19.3 versions prior to 19.3R2-S5, 19.3R3-S1; 19.4 versions prior to 19.4R1-S3, 19.4R2-S3, 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R1-S3 20.2R2; 20.3 versions prior to 20.3R1-S1, 20.3R2. Junos OS Evolved: All versions prior to 20.3R1-S1-EVO, 20.3R2-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

A logic vulnerability in the Juniper RPD (Routing Protocol Daemon) fails to properly validate unusual or exceptional conditions in BGP FlowSpec messages. An attacker sending valid BGP FlowSpec updates can trigger unexpected route advertisement changes within the BGP FlowSpec domain, causing persistent disruption to network traffic and a sustained DoS condition.

MitigationApply vendor-provided patches for the specific Junos OS/Evolved versions listed in the advisory, or implement BGP FlowSpec route filtering/validation at edge routers to reject untrusted FlowSpec announcements.

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= 18.1= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2
Junos Os EvolvedOperating system
Affected:= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3

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
None
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/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 installed Junos version
    Run 'show version' or 'show version detail' on the Juniper device CLI to obtain the exact Junos OS or Junos OS Evolved version
    Affected if The version matches any of: 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2 (Junos) or 19.2, 19.3, 19.4, 20.1, 20.2, 20.3 (Junos Evolved)
  2. Verify BGP is configured
    Run 'show bgp summary' or 'show configuration protocols bgp' to check if BGP is enabled on the device
    Affected if BGP is actively configured or operational on the device
  3. Confirm BGP FlowSpec is enabled
    Run 'show flowspec' or 'show configuration protocols bgp flow' to check for BGP FlowSpec configuration and operational status
    Affected if BGP FlowSpec is configured or active on any BGP peer or group
  4. Check for FlowSpec routes in the routing table
    Run 'show route table inet.0 flowspec' or 'show route flowspec detail' to inspect installed FlowSpec routes
    Affected if Any FlowSpec routes are present in the routing table

The device is affected if it runs an affected Junos/Evolved version AND has BGP FlowSpec enabled, regardless of whether malicious FlowSpec updates have been received.

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 vendor-provided patches for the specific Junos OS/Evolved versions listed in the advisory, or implement BGP FlowSpec route filtering/validation at edge routers to reject untrusted FlowSpec announcements.

Recommended fix High confidence

Junos OS Evolved: upgrade to 20.3R2-EVO (or 20.3R1-S1-EVO); Junos OS: upgrade to 20.3R2 or 20.3R1-S1

  1. 1. Identify the current Junos OS or Junos OS Evolved version running on the affected device using 'show version' command.
  2. 2. Review the Juniper Networks KB article at kb.juniper.net for complete version compatibility and specific patch requirements.
  3. 3. Plan maintenance window as the upgrade will require a system reboot.
  4. 4. Download the appropriate fixed Junos OS or Junos OS Evolved release (20.3R1-S1 or later for Junos OS; 20.3R1-S1-EVO or 20.3R2-EVO for Junos OS Evolved) from the Juniper Networks support portal.
  5. 5. Upload the new Junos image to the device using 'request system software add' command.
  6. 6. Reboot the device to apply the new software version using 'request system reboot' command.
  7. 7. After reboot, verify the new version is running with 'show version' and confirm BGP functionality is operational.
  8. 8. Monitor the device for any recurring DoS symptoms related to BGP FlowSpec processing.
Caveat Upgrading Junos OS may introduce changes in other features; ensure compatibility with existing network configurations and test in lab environment before production deployment

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

Fix this in Junos Scoped from the published advisory
  • Consultation8.0 h
  • Implementation16.0 h
  • Testing12.0 h
  • Review / QA8.0 h
44.0 hours of engineering $7,720
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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-2021-0211 in production — separate from our analysis above.

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