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JunosOperating system · Juniper

CVE-2021-31370

MEDIUM · 6.5 CVSS v3.1 Published 2021-10-19
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
70/100
Remediation priority · Elevated
No privileges Zero-click Patch available

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 Incomplete List of Disallowed Inputs vulnerability in Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on QFX5000 Series and EX4600 Series allows an adjacent unauthenticated attacker which sends a high rate of specific multicast traffic to cause control traffic received from the network to be dropped. This will impact control protocols (including but not limited to routing-protocols) and lead to a Denial of Service (DoS). Continued receipt of this specific multicast traffic will create a sustained Denial of Service (DoS) condition. This issue affects Juniper Networks Junos OS on QFX5000 and EX4600 Series: All versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R3-S5; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S3; 19.4 versions prior to 19.4R1-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2-S2, 20.4R3; 21.1 versions prior to 21.1R1-S1, 21.1R2.

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

A detailed technical summary for this CVE is being prepared.

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= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3= 20.4

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

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
Patch available Apply the vendor patch
Vendor patch kb.juniper.net →
Recommended fix High confidence

17.3R3-S12, 17.4R3-S5, 18.3R3-S5, or 18.4R3-S9 depending on your current release train

  1. 1. Identify the current Junos OS version on the affected QFX5000 Series or EX4600 Series switch using 'show version'
  2. 2. Based on the current version, upgrade to the appropriate fixed release: For 17.3.x upgrade to 17.3R3-S12 or later; For 17.4.x upgrade to 17.4R3-S5 or later; For 18.3.x upgrade to 18.3R3-S5 or later; For 18.4.x upgrade to 18.4R3-S9 or later
  3. 3. Download the appropriate Junos OS upgrade package from the Juniper Networks download portal
  4. 4. Upload the upgrade package to the switch and initiate the upgrade using 'request system software add <package>'
  5. 5. Reboot the device after upgrade completes using 'request system reboot'
  6. 6. Verify the new version is installed using 'show version' and confirm the fix is applied
  7. 7. Monitor for any control protocol issues and verify normal operation of routing protocols
Caveat Standard Junos upgrade precautions apply - verify hardware compatibility, schedule maintenance window as upgrade causes reboot, backup configuration

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

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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-2021-31370 in production — separate from our analysis above.

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