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JunosOperating system · Juniper

CVE-2021-31367

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
A Missing Release of Memory after Effective Lifetime vulnerability in the Packet Forwarding Engine (PFE) of Juniper Networks Junos OS on PTX Series allows an adjacent attacker to cause a Denial of Service (DoS) by sending genuine BGP flowspec packets which cause an FPC heap memory leak. Once having run out of memory the FPC will crash and restart along with a core dump. Continued receipted of these packets will create a sustained Denial of Service (DoS) condition. This issue affects: Juniper Networks Junos OS All versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S7; 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-S6; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R3-S1; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R2. Juniper Networks Junos Evolved is not affected.

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
How this class of weakness works · CWE-401

Allocated memory is never released on some path, so a long-running service or a repeatedly triggered request steadily consumes memory until performance degrades or the process crashes. Attackers exploit it by simply driving the leaking path. Remediation is pairing every allocation with a release and using ownership patterns or tooling to catch what leaks.

General guidance for the memory leak class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

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:= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3= 20.4= 21.1

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

Upgrade to 18.4R3-S9 or later (for 18.4 branch), 19.1R3-S7 (for 19.1), 19.2R3-S3 (for 19.2), 19.3R3-S3 (for 19.3), or ideally the latest stable release such as 20.4R3 or 21.1R2

  1. 1. Identify the current Junos OS version running on the PTX Series device using 'show version'
  2. 2. Determine the appropriate fixed release based on your current version branch from the vendor advisory (18.4R3-S9, 19.1R3-S7, 19.2R3-S3, 19.3R3-S3, 19.4R3-S6, 20.1R3, 20.2R3-S1, 20.3R3, 20.4R3, or 21.1R2)
  3. 3. Download the appropriate Junos OS software image from the Juniper Networks support portal
  4. 4. Upload the software image to the device using 'file copy' or USB storage
  5. 5. Install the new software using 'request system software add <package-name> reboot'
  6. 6. After reboot, verify the new version is installed with 'show version' and confirm the memory leak is resolved
Caveat Standard Junos upgrade considerations apply - review release notes for compatibility and ensure configuration backup before upgrade

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-2021-31367 in production — separate from our analysis above.

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