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JunosOperating system · Juniper

CVE-2021-31382

CRITICAL · 9.0 CVSS v3.1 Published 2021-10-19
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
99/100
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
On PTX1000 System, PTX10002-60C System, after upgrading to an affected release, a Race Condition vulnerability between the chassis daemon (chassisd) and firewall process (dfwd) of Juniper Networks Junos OS, may update the device's interfaces with incorrect firewall filters. This issue only occurs when upgrading the device to an affected version of Junos OS. Interfaces intended to have protections may have no protections assigned to them. Interfaces with one type of protection pattern may have alternate protections assigned to them. Interfaces intended to have no protections may have protections assigned to them. These firewall rule misassignments may allow genuine traffic intended to be stopped at the interface to propagate further, potentially causing disruptions in services by propagating unwanted traffic. An attacker may be able to take advantage of these misassignments. This issue affects Juniper Networks Junos OS on PTX1000 System: 17.2 versions 17.2R1 and later versions prior to 17.3 versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R1-S8, 18.4R2-S8, 18.4R3-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-S3; 19.4 versions prior to 19.4R2-S4, 19.4R3-S3; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R2-S3, 20.2R3; 20.3 versions prior to 20.3R2-S1, 20.3R3; 20.4 versions prior to 20.4R1-S1, 20.4R2. This issue does not affect Juniper Networks Junos OS prior to version 17.2R1 on PTX1000 System. This issue affects Juniper Networks Junos OS on PTX10002-60C System: 18.2 versions 18.2R1 and later versions prior to 18.4 versions prior to 18.4R3-S9; 19.1 versions later than 19.1R1 prior to 19.4 versions prior to 19.4R2-S5, 19.4R3-S5; 20.1 versions prior to 20.1R3-S1; 20.2 versions prior to 20.2R3-S2; 20.3 versions prior to 20.3R3-S1; 20.4 versions 20.4R1 and later versions prior to 21.1 versions prior to 21.1R2; 21.2 versions 21.2R1 and later versions prior to 21.3 versions prior to 21.3R2. This issue does not affect Juniper Networks Junos OS prior to version 18.2R1 on PTX10002-60C System. This issue impacts all filter families (inet, inet6, etc.) and all loopback filters. It does not rely upon the location where a filter is set, impacting both logical and physical interfaces.

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 race condition vulnerability between the chassis daemon (chassisd) and firewall process (dfwd) in Juniper Junos OS causes incorrect firewall filter assignments to interfaces after upgrading affected devices. This leads to three failure modes: protected interfaces lose their filters, interfaces receive wrong filter types, or unprotected interfaces incorrectly receive filters. The issue affects all filter families (inet, inet6) and impacts both logical and physical interfaces on PTX1000 and PTX10002-60C systems.

MitigationUpgrade Junos OS to the fixed versions specified in the advisory. After upgrade, verify all firewall filter assignments are correctly applied to intended interfaces, as filters may need to be reconfigured if misassigned during the upgrade process.

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:= 17.2= 17.2x75= 17.3= 17.4= 18.1= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4

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
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/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 hardware model
    Run 'show chassis hardware' or 'show version' to confirm the device model is PTX1000 or PTX10002-60C
    Affected if Device model is PTX1000 or PTX10002-60C
  2. Check Junos OS version
    Run 'show version' and compare the installed Junos version against the affected list: 17.2, 17.2x75, 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4
    Affected if Installed version matches one of the affected versions listed
  3. Verify firewall filter configuration
    Run 'show configuration firewall' to list all defined firewall filters, then run 'show configuration interfaces <interface-name> family <inet|inet6> filter' to check which filters are applied to each interface
    Affected if Firewall filters are configured on interfaces (the race condition affects filter assignments)
  4. Confirm filter-to-interface binding correctness
    For each interface with a filter, run 'show interface <interface-name> extensive | grep filter' or 'show firewall' to verify the applied filter matches the intended configuration
    Affected if Any interface shows a filter that does not match the configured assignment, or a protected interface shows no filter, or an unprotected interface shows an unexpected filter

Device is affected if it is a PTX1000 or PTX10002-60C running an affected Junos version AND firewall filter assignments do not match the intended configuration.

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

Upgrade Junos OS to the fixed versions specified in the advisory. After upgrade, verify all firewall filter assignments are correctly applied to intended interfaces, as filters may need to be reconfigured if misassigned during the upgrade process.

Recommended fix High confidence

Upgrade to the latest service release in your version branch: PTX1000 - 17.3R3-S12 or later for 17.2.x, 17.4R3-S5 or later for 17.4.x, 18.1R3-S13 or later for 18.1.x, 18.2R3-S8 or later for 18.2.x, 18.3R3-S5 or later for 18.3.x, 18.4R3-S8 or later for 18.4.x, 19.1R3-S5 or later for 19.1.x, 19.2R3-S2

  1. 1. Identify the current Junos OS version on the PTX1000 or PTX10002-60C device using 'show version'
  2. 2. Determine the appropriate fixed release based on the current version branch (e.g., for 17.2.x upgrade to 17.3R3-S12, for 17.4.x upgrade to 17.4R3-S5)
  3. 3. Download the appropriate Junos OS service release from the Juniper Networks website
  4. 4. Before upgrading, backup the current configuration using 'request system configuration backup'
  5. 5. Upload the new Junos OS package to the device using 'request system software add <package>'
  6. 6. Reboot the device using 'request system reboot'
  7. 7. After reboot, verify the new Junos OS version is installed using 'show version'
  8. 8. Verify firewall filter assignments are correct using 'show firewall' and 'show interfaces <interface> filter'
Caveat Standard Junos OS upgrade considerations apply - review release notes for any known issues, configuration compatibility notes, and ensure proper configuration backup before upgrade

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

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing8.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,800
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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-2021-31382 in production — separate from our analysis above.

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What this is

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