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JunosOperating system · Juniper

CVE-2021-0291

MEDIUM · 6.5 CVSS v3.1 Published 2021-07-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
74/100
Remediation priority · Elevated
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 Exposure of System Data vulnerability in Juniper Networks Junos OS and Junos OS Evolved, where a sensitive system-level resource is not being sufficiently protected, allows a network-based unauthenticated attacker to send specific traffic which partially reaches this resource. A high rate of specific traffic may lead to a partial Denial of Service (DoS) as the CPU utilization of the RE is significantly increased. The SNMP Agent Extensibility (agentx) process should only be listening to TCP port 705 on the internal routing instance. External connections destined to port 705 should not be allowed. This issue affects: Juniper Networks Junos OS: 15.1 versions prior to 15.1R7-S9; 17.3 versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R2-S13, 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R2-S8; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R3-S2; 19.3 versions prior to 19.3R2-S6, 19.3R3-S2; 19.4 versions prior to 19.4R1-S4, 19.4R2-S4, 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2; 20.3 versions prior to 20.3R2. Juniper Networks Junos OS Evolved versions prior to 20.3R2-EVO. This issue does not affect Juniper Networks Junos OS versions prior to 13.2R1.

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 network-based unauthenticated attacker can send traffic to TCP port 705 (SNMP Agent Extensibility/agentx) which should only be accessible via internal routing instances. This causes high CPU utilization on the Routing Engine, leading to partial DoS. The agentx process is exposed externally when it should be restricted to internal communications only.

MitigationConfigure firewall filters to block external traffic destined for TCP port 705 and ensure the agentx process only binds to internal routing instances. Apply vendor patches for affected Junos OS versions.

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:= 15.1= 17.3= 17.4= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3
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
Unchanged
Confidentiality
Low
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L

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. Check the installed Junos OS version
    Run 'show version' or 'request system version' to obtain the exact Junos version running on the device
    Affected if The installed version matches one of the affected versions listed: 15.1, 17.3, 17.4, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3 for Junos OS or Junos OS Evolved
  2. Verify if TCP port 705 is accessible from external networks
    Run 'show system services listening-on' or use 'netstat -an | grep 705' from the device CLI to determine if the agentx service is bound to external interfaces
    Affected if The agentx process (port 705) is bound to any interface accessible from outside the internal routing instance
  3. Inspect firewall filter configurations for port 705
    Run 'show firewall' and review filter terms to check if there are explicit blocks or filters applied to TCP port 705 from external sources
    Affected if No firewall filter exists to block external traffic destined for TCP port 705, or the existing filters allow such traffic
  4. Check agentx process binding configuration
    Run 'show configuration | display set | match agentx' to review the agentx configuration and determine if it is restricted to internal routing instances
    Affected if The agentx process is configured to accept external connections or is not restricted to internal-only communication

The device is affected if it runs an affected Junos version AND TCP port 705 (agentx) is exposed to external networks without proper firewall filtering to block such traffic.

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

Configure firewall filters to block external traffic destined for TCP port 705 and ensure the agentx process only binds to internal routing instances. Apply vendor patches for affected Junos OS versions.

Fix this in Junos Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,090
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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-2021-0291 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