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JunosOperating system · Juniper

CVE-2021-31353

HIGH · 7.5 CVSS v3.1 Published 2021-10-19
Fix available
A fix is available. Upgrade to after 20.3 or later.
See remediation →
84/100
Remediation priority · High
Public exploit 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 Handling of Exceptional Conditions vulnerability in Juniper Networks Junos OS and Junos OS Evolved allows an attacker to inject a specific BGP update, causing the routing protocol daemon (RPD) to crash and restart, leading to a Denial of Service (DoS). Continued receipt and processing of the BGP update will create a sustained Denial of Service (DoS) condition. This issue affects very specific versions of Juniper Networks Junos OS: 19.3R3-S2; 19.4R3-S3; 20.2 versions 20.2R2-S3 and later, prior to 20.2R3-S2; 20.3 versions 20.3R2 and later, prior to 20.3R3; 20.4 versions 20.4R2 and later, prior to 20.4R3; 21.1 versions prior to 21.1R2. Juniper Networks Junos OS 20.1 is not affected by this issue. This issue also affects Juniper Networks Junos OS Evolved: All versions prior to 20.4R2-S3-EVO, 20.4R3-EVO; 21.1-EVO versions prior to 21.1R2-EVO; 21.2-EVO versions prior to 21.2R2-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

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:= 19.3= 19.4= 20.2= 20.3= 20.4= 21.1
Junos Os EvolvedOperating system
Affected:<= 20.3= 20.4= 21.1= 21.2

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

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
Upgrade available Upgrade to a release after 20.3
Recommended fix High confidence

Junos OS: 20.2R3-S2, 20.3R3, 20.4R3, or 21.1R2+ | Junos OS Evolved: 20.4R2-S3-EVO, 20.4R3-EVO, 21.1R2-EVO, or 21.2R2-EVO+

  1. 1. Identify the current Junos OS or Junos OS Evolved version running on the device using 'show version'
  2. 2. For Junos OS: upgrade to one of the fixed versions: 20.2R3-S2 or later, 20.3R3 or later, 20.4R3 or later, or 21.1R2 or later
  3. 3. For Junos OS Evolved: upgrade to one of the fixed versions: 20.4R2-S3-EVO, 20.4R3-EVO, 21.1R2-EVO, or 21.2R2-EVO or later
  4. 4. Download the appropriate Junos upgrade image from the Juniper Networks support portal
  5. 5. Upload the upgrade image to the device using 'request system software add' command
  6. 6. Reboot the device after upgrade completes using 'request system reboot'
  7. 7. Verify the RPD process is running and BGP peers are established after reboot using 'show bgp summary'
Caveat Standard Junos upgrade precautions apply - verify hardware compatibility and ensure valid configuration backup exists before upgrading

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

We can identify the exact fixed release, upgrade, and verify it in staging — typical engagement from $1,950. Get the upgrade done

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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-2021-31353 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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